diff --git a/.github/workflows/oop.yml b/.github/workflows/oop.yml
index 291d7cc..44bee24 100644
--- a/.github/workflows/oop.yml
+++ b/.github/workflows/oop.yml
@@ -17,7 +17,13 @@ jobs:
         working-directory: ./${{ github.event.pull_request.title }}
     steps:
       - uses: actions/checkout@v3
-      
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'oracle'
+
       - name: Setup Gradle
         uses: gradle/gradle-build-action@v2
 
diff --git a/Task_1_3/build.gradle b/Task_1_3/build.gradle
new file mode 100644
index 0000000..e892fe9
--- /dev/null
+++ b/Task_1_3/build.gradle
@@ -0,0 +1,30 @@
+plugins {
+    id 'java'
+    id 'jacoco'
+}
+
+group = 'ru.nsu.sharapov'
+version = '1.0-SNAPSHOT'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation platform('org.junit:junit-bom:5.9.1')
+    testImplementation 'org.junit.jupiter:junit-jupiter'
+}
+
+test {
+    useJUnitPlatform()
+}
+
+jacocoTestReport {
+    reports {
+        xml.required = true
+    }
+}
+
+compileJava.options.encoding = "UTF-8"
+compileTestJava.options.encoding = "UTF-8"
+javadoc.options.encoding = "UTF-8"
diff --git a/Task_1_3/gradle/wrapper/gradle-wrapper.jar b/Task_1_3/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..1b33c55
Binary files /dev/null and b/Task_1_3/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/Task_1_3/gradle/wrapper/gradle-wrapper.properties b/Task_1_3/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..ca025c8
--- /dev/null
+++ b/Task_1_3/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/Task_1_3/gradlew b/Task_1_3/gradlew
new file mode 100644
index 0000000..23d15a9
--- /dev/null
+++ b/Task_1_3/gradlew
@@ -0,0 +1,251 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH="\\\"\\\""
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/Task_1_3/gradlew.bat b/Task_1_3/gradlew.bat
new file mode 100644
index 0000000..5eed7ee
--- /dev/null
+++ b/Task_1_3/gradlew.bat
@@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/Task_1_3/settings.gradle b/Task_1_3/settings.gradle
new file mode 100644
index 0000000..5014f97
--- /dev/null
+++ b/Task_1_3/settings.gradle
@@ -0,0 +1 @@
+rootProject.name = 'Task_1_3'
\ No newline at end of file
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Add.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Add.java
new file mode 100644
index 0000000..4172f51
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Add.java
@@ -0,0 +1,77 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Subclass of addition operation.
+ */
+public class Add extends BinaryOperation {
+
+    /**
+     * Constructor.
+     *
+     * @param left  Left expression
+     * @param right Right expression
+     */
+    public Add(Expression left, Expression right) {
+        super(left, right);
+    }
+
+    /**
+     * Get Add sign.
+     *
+     * @return '+'
+     */
+    @Override
+    public char getSign() {
+        return '+';
+    }
+
+
+    /**
+     * Take derivative by variable.
+     *
+     * @param variable String variable
+     * @return New expression of the resulting derivative
+     */
+    @Override
+    public Expression derivative(String variable) {
+        return new Add(left.derivative(variable), right.derivative(variable));
+    }
+
+    /**
+     * Addition evaluation.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Result of evaluation
+     */
+    @Override
+    public double evalMapped(Map<String, Integer> varsValues) {
+        return left.evalMapped(varsValues) + right.evalMapped(varsValues);
+    }
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    @Override
+    public Expression simplify() {
+        Expression simplifiedLeft = left.simplify();
+        Expression simplifiedRight = right.simplify();
+        Number zero = new Number(0);
+        if (simplifiedLeft instanceof Number a && simplifiedRight instanceof Number b) {
+            return new Number(a.getValue() + b.getValue());
+        }
+        if (Objects.equals(simplifiedLeft, zero)) {
+            return simplifiedRight;
+        }
+        if (Objects.equals(simplifiedRight, zero)) {
+            return simplifiedLeft;
+        }
+        return new Add(simplifiedLeft, simplifiedRight);
+    }
+
+
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/BinaryOperation.java b/Task_1_3/src/main/java/ru/nsu/sharapov/BinaryOperation.java
new file mode 100644
index 0000000..8514b59
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/BinaryOperation.java
@@ -0,0 +1,85 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+
+/**
+ * Superclass of binary operations: add, sub, mul, div.
+ */
+public abstract class BinaryOperation extends Expression {
+
+    protected Expression left;
+    protected Expression right;
+
+    /**
+     * Constructor of binary expression.
+     *
+     * @param left  Left expression
+     * @param right Right expression
+     */
+    public BinaryOperation(Expression left, Expression right) {
+        this.left = left;
+        this.right = right;
+    }
+
+    /**
+     * Right expression setter.
+     *
+     * @param right Right expression
+     */
+    public void setRight(Expression right) {
+        this.right = right;
+    }
+
+    /**
+     * String representation of binary expression.
+     *
+     * @return string representation
+     */
+    @Override
+    public String toString() {
+        return "(" + left + getSign() + right + ")";
+    }
+
+    /**
+     * Get operation sign.
+     *
+     * @return operation sign symbol
+     */
+    public abstract char getSign();
+
+    /**
+     * Take derivative by variable.
+     *
+     * @param variable String variable
+     * @return New expression of the resulting derivative
+     */
+    @Override
+    public abstract Expression derivative(String variable);
+
+    /**
+     * Expression evaluation.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Result of evaluation
+     */
+    @Override
+    public abstract double evalMapped(Map<String, Integer> varsValues);
+
+    /**
+     * Equality of binary expressions.
+     *
+     * @param obj the reference object with which to compare.
+     * @return equal or not
+     */
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        } else if (obj instanceof BinaryOperation other) {
+            return this.left.equals(other.left) && this.right.equals(other.right)
+                && this.getSign() == other.getSign();
+        } else {
+            return false;
+        }
+    }
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Div.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Div.java
new file mode 100644
index 0000000..8f4167c
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Div.java
@@ -0,0 +1,73 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Subclass of division operation.
+ */
+public class Div extends BinaryOperation {
+
+    /**
+     * Constructor.
+     *
+     * @param left  Left expression
+     * @param right Right expression
+     */
+    public Div(Expression left, Expression right) {
+        super(left, right);
+    }
+
+    /**
+     * Get Div sign.
+     *
+     * @return '/'
+     */
+    @Override
+    public char getSign() {
+        return '/';
+    }
+
+    /**
+     * Take derivative by variable.
+     *
+     * @param variable String variable
+     * @return New expression of the resulting derivative
+     */
+    @Override
+    public Expression derivative(String variable) {
+        return new Div(new Sub(new Mul(left.derivative(variable), right),
+            new Mul(left, right.derivative(variable))), new Mul(right, right));
+    }
+
+    /**
+     * Division evaluation.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Result of evaluation
+     */
+    @Override
+    public double evalMapped(Map<String, Integer> varsValues) {
+        return left.evalMapped(varsValues) / right.evalMapped(varsValues);
+    }
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    @Override
+    public Expression simplify() {
+        Expression simplifiedLeft = left.simplify();
+        Expression simplifiedRight = right.simplify();
+        Number zero = new Number(0);
+        Number one = new Number(1);
+        if (Objects.equals(simplifiedLeft, zero)) {
+            return zero;
+        }
+        if (Objects.equals(simplifiedRight, one)) {
+            return simplifiedLeft;
+        }
+        return new Div(simplifiedLeft, simplifiedRight);
+    }
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Expression.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Expression.java
new file mode 100644
index 0000000..03747bc
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Expression.java
@@ -0,0 +1,93 @@
+package ru.nsu.sharapov;
+
+import java.io.PrintWriter;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.NoSuchElementException;
+
+/**
+ * Abstract class of expression.
+ */
+public abstract class Expression {
+
+    /**
+     * Static method to parse string of variables and their values into Map: Variable -> Value.
+     *
+     * @param values String of variables and their values, for example: "x = 10; y = 13"
+     * @return Map: String variable -> Integer value
+     */
+    protected static Map<String, Integer> parseVariables(String values) {
+        Map<String, Integer> map = new HashMap<>();
+        if (!values.contains(";")) {
+            return map;
+        }
+
+        for (String part : values.split(";")) {
+            String[] keyValue = part.split("=");
+            String key = keyValue[0].trim();
+            Integer value = Integer.parseInt(keyValue[1].trim());
+            map.put(key, value);
+        }
+        return map;
+    }
+
+    /**
+     * Abstract print.
+     *
+     * @param writer Writer to the file or console
+     */
+    public void print(PrintWriter writer) {
+        writer.print(this);
+    }
+
+    /**
+     * String representation of expressions.
+     *
+     * @return string representation
+     */
+    public abstract String toString();
+
+    /**
+     * Abstract derivative.
+     *
+     * @param variable String variable
+     * @return New expression of the resulting derivative
+     */
+    public abstract Expression derivative(String variable);
+
+    /**
+     * Abstract evaluation with mapped variables and their values.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Result of evaluation
+     * @throws NoSuchElementException if required variable is not found in varsValues
+     */
+    protected abstract double evalMapped(Map<String, Integer> varsValues)
+        throws NoSuchElementException;
+
+    /**
+     * Abstract evaluation.
+     *
+     * @param varsValues String of variables and their values, for example: "x = 10; y = 13"
+     * @return result of evaluation
+     * @throws NoSuchElementException if required variable is not found in varsValues
+     */
+    public double eval(String varsValues) throws NoSuchElementException {
+        return evalMapped(parseVariables(varsValues));
+    }
+
+    /**
+     * Abstract equality of expressions.
+     *
+     * @param obj the reference object with which to compare.
+     * @return equal or not
+     */
+    public abstract boolean equals(Object obj);
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    public abstract Expression simplify();
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Main.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Main.java
new file mode 100644
index 0000000..7ce9c49
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Main.java
@@ -0,0 +1,15 @@
+package ru.nsu.sharapov;
+
+import java.io.PrintWriter;
+
+
+public class Main {
+
+    public static void main(String[] args) {
+        PrintWriter consoleWriter = new PrintWriter(System.out);
+        for (String strExpr : args) {
+            Expression expr = Parser.buildExpr(strExpr);
+            expr.print(consoleWriter);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Mul.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Mul.java
new file mode 100644
index 0000000..314bd76
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Mul.java
@@ -0,0 +1,73 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Subclass of multiplication operation.
+ */
+public class Mul extends BinaryOperation {
+
+    /**
+     * Constructor.
+     *
+     * @param left  Left expression
+     * @param right Right expression
+     */
+    public Mul(Expression left, Expression right) {
+        super(left, right);
+    }
+
+    /**
+     * Get Mul sign.
+     *
+     * @return '*'
+     */
+    @Override
+    public char getSign() {
+        return '*';
+    }
+
+    @Override
+    public Expression derivative(String variable) {
+        return new Add(new Mul(left.derivative(variable), right),
+            new Mul(left, right.derivative(variable)));
+    }
+
+    /**
+     * Multiplication evaluation.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Result of evaluation
+     */
+    @Override
+    public double evalMapped(Map<String, Integer> varsValues) {
+        return left.evalMapped(varsValues) * right.evalMapped(varsValues);
+    }
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    @Override
+    public Expression simplify() {
+        Expression simplifiedLeft = left.simplify();
+        Expression simplifiedRight = right.simplify();
+        Number zero = new Number(0);
+        Number one = new Number(1);
+        if (left instanceof Number a && right instanceof Number b) {
+            return new Number(a.getValue() * b.getValue());
+        }
+        if (Objects.equals(simplifiedLeft, zero) || Objects.equals(simplifiedRight, zero)) {
+            return zero;
+        }
+        if (Objects.equals(simplifiedLeft, one)) {
+            return simplifiedRight;
+        }
+        if (Objects.equals(simplifiedRight, one)) {
+            return simplifiedLeft;
+        }
+        return new Mul(simplifiedLeft, simplifiedRight);
+    }
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Number.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Number.java
new file mode 100644
index 0000000..90263f6
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Number.java
@@ -0,0 +1,88 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+
+/**
+ * Subclass of constant number.
+ */
+public class Number extends Expression {
+
+    private final int value;
+
+    /**
+     * Constructor.
+     *
+     * @param value Number value
+     */
+    public Number(int value) {
+        this.value = value;
+    }
+
+    /**
+     * String representation of number.
+     *
+     * @return string representation
+     */
+    @Override
+    public String toString() {
+        return String.valueOf(value);
+    }
+
+    /**
+     * Derivative of a number.
+     *
+     * @param variable String variable
+     * @return Number object with zero value
+     */
+    @Override
+    public Expression derivative(String variable) {
+        return new Number(0);
+    }
+
+    /**
+     * Evaluation of a number.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Number value
+     */
+    @Override
+    public double evalMapped(Map<String, Integer> varsValues) {
+        return value;
+    }
+
+    /**
+     * Number value getter.
+     *
+     * @return value
+     */
+    public int getValue() {
+        return this.value;
+    }
+
+    /**
+     * Equality of numbers.
+     *
+     * @param obj the reference object with which to compare.
+     * @return equal or not
+     */
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        } else if (obj instanceof Number other) {
+            return this.value == other.value;
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    @Override
+    public Expression simplify() {
+        return this;
+    }
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Parser.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Parser.java
new file mode 100644
index 0000000..70d7d90
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Parser.java
@@ -0,0 +1,71 @@
+package ru.nsu.sharapov;
+
+import java.util.Stack;
+
+public class Parser {
+
+    /**
+     * Expression object builder by string.
+     *
+     * @param string String expression
+     * @return New expression
+     */
+    public static Expression buildExpr(String string) {
+        StringBuilder number = new StringBuilder();
+        StringBuilder variable = new StringBuilder();
+        Stack<Expression> stack = new Stack<>();
+        for (char symbol : string.toCharArray()) {
+
+            if (Character.isDigit(symbol)) {
+                variable = new StringBuilder();
+                if (!stack.isEmpty() && stack.peek() instanceof Number) {
+                    stack.pop();
+                }
+                number.append(symbol);
+                stack.add(new Number(Integer.parseInt(String.valueOf(number))));
+            } else if (Character.isLetter(symbol)) {
+                number = new StringBuilder();
+                if (!stack.isEmpty() && stack.peek() instanceof Variable) {
+                    stack.pop();
+                }
+                variable.append(symbol);
+                stack.add(new Variable(String.valueOf(variable)));
+            } else {
+                number = new StringBuilder();
+                variable = new StringBuilder();
+                switch (symbol) {
+                    case '(':
+                        stack.add(null);
+                        break;
+                    case ')':
+                        Expression right = stack.pop();
+                        try {
+                            BinaryOperation exprWithoutRight = (BinaryOperation) stack.pop();
+                            stack.pop(); // null "("
+                            exprWithoutRight.setRight(right);
+                            stack.add(exprWithoutRight);
+                        } catch (ClassCastException exception) {
+                            throw new ClassCastException("Expected BinaryOperation");
+                        }
+                        break;
+                    case ('+'):
+                        stack.add(new Add(stack.pop(), null));
+                        break;
+                    case ('-'):
+                        stack.add(new Sub(stack.pop(), null));
+                        break;
+                    case ('*'):
+                        stack.add(new Mul(stack.pop(), null));
+                        break;
+                    case ('/'):
+                        stack.add(new Div(stack.pop(), null));
+                        break;
+                    default:
+                        throw new IllegalArgumentException("Unexpected character: " + symbol);
+
+                }
+            }
+        }
+        return stack.pop();
+    }
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Sub.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Sub.java
new file mode 100644
index 0000000..453c311
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Sub.java
@@ -0,0 +1,62 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Subclass of subtraction operation.
+ */
+public class Sub extends BinaryOperation {
+
+    public Sub(Expression left, Expression right) {
+        super(left, right);
+    }
+
+    /**
+     * Get Sub sign.
+     *
+     * @return '-'
+     */
+    @Override
+    public char getSign() {
+        return '-';
+    }
+
+    @Override
+    public Expression derivative(String variable) {
+        return new Sub(left.derivative(variable), right.derivative(variable));
+    }
+
+    /**
+     * Subtraction evaluation.
+     *
+     * @param varsValues Map of variables and their values
+     * @return Result of evaluation
+     */
+    @Override
+    public double evalMapped(Map<String, Integer> varsValues) {
+        return left.evalMapped(varsValues) - right.evalMapped(varsValues);
+    }
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    @Override
+    public Expression simplify() {
+        Expression simplifiedLeft = left.simplify();
+        Expression simplifiedRight = right.simplify();
+        Number zero = new Number(0);
+        if (simplifiedLeft instanceof Number a && simplifiedRight instanceof Number b) {
+            return new Number(a.getValue() - b.getValue());
+        }
+        if (Objects.equals(simplifiedLeft, simplifiedRight)) {
+            return zero;
+        }
+        if (Objects.equals(simplifiedRight, zero)) {
+            return simplifiedLeft;
+        }
+        return new Sub(simplifiedLeft, simplifiedRight);
+    }
+}
diff --git a/Task_1_3/src/main/java/ru/nsu/sharapov/Variable.java b/Task_1_3/src/main/java/ru/nsu/sharapov/Variable.java
new file mode 100644
index 0000000..b2090db
--- /dev/null
+++ b/Task_1_3/src/main/java/ru/nsu/sharapov/Variable.java
@@ -0,0 +1,89 @@
+package ru.nsu.sharapov;
+
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+
+/**
+ * Subclass of variable.
+ */
+public class Variable extends Expression {
+
+    private final String name;
+
+    /**
+     * Constructor.
+     *
+     * @param name Variable name
+     */
+    public Variable(String name) {
+        this.name = name;
+    }
+
+    /**
+     * String representation of variable.
+     *
+     * @return string representation
+     */
+    @Override
+    public String toString() {
+        return name;
+    }
+
+    /**
+     * Derivative of a variable.
+     *
+     * @param variable String variable
+     * @return Number object
+     */
+    @Override
+    public Expression derivative(String variable) {
+        if (this.name.equals(variable)) {
+            return new Number(1);
+        } else {
+            return new Number(0);
+        }
+    }
+
+    /**
+     * Evaluation of a variable
+     *
+     * @param varsValues Map of variables and their values
+     * @return Variable value
+     * @throws NoSuchElementException if required variable is not found in varsValues
+     */
+    @Override
+    public double evalMapped(Map<String, Integer> varsValues) throws NoSuchElementException {
+        if (!varsValues.containsKey(name)) {
+            throw new NoSuchElementException("Variable \"" + name + "\" is undefined.");
+        }
+        return varsValues.get(name);
+    }
+
+    /**
+     * Equality of variables.
+     *
+     * @param obj the reference object with which to compare
+     * @return variable names equal or not
+     */
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        } else if (obj instanceof Variable other) {
+            return Objects.equals(this.name, other.name);
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * Simplifies expression.
+     *
+     * @return simplified expression
+     */
+    @Override
+    public Expression simplify() {
+        return this;
+    }
+}
diff --git a/Task_1_3/src/test/java/ru/nsu/sharapov/BuildTest.java b/Task_1_3/src/test/java/ru/nsu/sharapov/BuildTest.java
new file mode 100644
index 0000000..e66a3ef
--- /dev/null
+++ b/Task_1_3/src/test/java/ru/nsu/sharapov/BuildTest.java
@@ -0,0 +1,54 @@
+package ru.nsu.sharapov;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static ru.nsu.sharapov.Parser.buildExpr;
+
+import org.junit.jupiter.api.Test;
+
+public class BuildTest {
+
+    @Test
+    void add() {
+        String strExpr = "((a+b)+128)";
+        Expression actual = buildExpr(strExpr);
+        Expression expected = new Add(new Add(new Variable("a"), new Variable("b")),
+            new Number(128));
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void sub() {
+        String strExpr = "(128-(a-b))";
+        Expression actual = buildExpr(strExpr);
+        Expression expected = new Sub(new Number(128),
+            new Sub(new Variable("a"), new Variable("b")));
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mul() {
+        String strExpr = "(a*(b*128))";
+        Expression actual = buildExpr(strExpr);
+        Expression expected = new Mul(new Variable("a"),
+            new Mul(new Variable("b"), new Number(128)));
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void div() {
+        String strExpr = "(b/(a/128))";
+        Expression actual = buildExpr(strExpr);
+        Expression expected = new Div(new Variable("b"),
+            new Div(new Variable("a"), new Number(128)));
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void complex() {
+        String strExpr = "(((a+b)/(128*c))-8)";
+        Expression actual = buildExpr(strExpr);
+        Expression expected = new Sub(new Div(new Add(new Variable("a"), new Variable("b")),
+            new Mul(new Number(128), new Variable("c"))), new Number(8));
+        assertEquals(expected, actual);
+    }
+}
diff --git a/Task_1_3/src/test/java/ru/nsu/sharapov/DerivativeTest.java b/Task_1_3/src/test/java/ru/nsu/sharapov/DerivativeTest.java
new file mode 100644
index 0000000..ac2ac67
--- /dev/null
+++ b/Task_1_3/src/test/java/ru/nsu/sharapov/DerivativeTest.java
@@ -0,0 +1,75 @@
+package ru.nsu.sharapov;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static ru.nsu.sharapov.Parser.buildExpr;
+
+import org.junit.jupiter.api.Test;
+
+public class DerivativeTest {
+
+    @Test
+    void add() {
+        String strExpr = "(8+(a+b))";
+        Expression expr = buildExpr(strExpr);
+        Expression actual = expr.derivative("a").simplify();
+        Number expected = new Number(1);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void sub() {
+        String strExpr = "((a-8)-b)";
+        Expression expr = buildExpr(strExpr);
+        Expression actual = expr.derivative("b").simplify();
+        Number expected = new Number(-1);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mul() {
+        String strExpr = "((8*b)*a)";
+        Expression expr = buildExpr(strExpr);
+        Expression actual = expr.derivative("a").simplify();
+        Mul expected = new Mul(new Number(8), new Variable("b"));
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void div() {
+        String strExpr = "((a/b)/8)";
+        Expression expr = buildExpr(strExpr);
+        Expression actual = expr.derivative("b").simplify();
+        Div expected = new Div(new Mul(new Div(new Sub(new Number(0), new Variable("a")),
+            new Mul(new Variable("b"), new Variable("b"))), new Number(8)), new Number(64));
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void complex() {
+        String strExpr = "(((a*8)-(b+c))/(d*e))";
+        Expression expr = buildExpr(strExpr);
+        Expression actual = expr.derivative("e").simplify();
+        System.out.println(actual);
+        Div expected =
+            new Div(
+                new Sub(
+                    new Number(0),
+                    new Mul(
+                        new Sub(
+                            new Mul(
+                                new Variable("a"),
+                                new Number(8)),
+                            new Add(
+                                new Variable("b"),
+                                new Variable("c"))),
+                        new Variable("d"))),
+                new Mul(
+                    new Mul(
+                        new Variable("d"),
+                        new Variable("e")),
+                    new Mul(
+                        new Variable("d"),
+                        new Variable("e"))));
+        assertEquals(expected, actual);
+    }
+}
diff --git a/Task_1_3/src/test/java/ru/nsu/sharapov/EvalTest.java b/Task_1_3/src/test/java/ru/nsu/sharapov/EvalTest.java
new file mode 100644
index 0000000..65154b9
--- /dev/null
+++ b/Task_1_3/src/test/java/ru/nsu/sharapov/EvalTest.java
@@ -0,0 +1,79 @@
+package ru.nsu.sharapov;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static ru.nsu.sharapov.Parser.buildExpr;
+
+import java.util.NoSuchElementException;
+import org.junit.jupiter.api.Test;
+
+public class EvalTest {
+
+    @Test
+    void noVars() {
+        String strExpr = "(3+2)";
+        Expression expr = buildExpr(strExpr);
+        double actual = expr.eval("");
+        double expected = 5;
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void add() {
+        String strExpr = "(x+y)";
+        Expression expr = buildExpr(strExpr);
+        double actual = expr.eval("x = 10; y = 13");
+        double expected = 23;
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void sub() {
+        String strExpr = "(x-y)";
+        Expression expr = buildExpr(strExpr);
+        double actual = expr.eval("x = 10; y = 13");
+        double expected = -3;
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mul() {
+        String strExpr = "(x*y)";
+        Expression expr = buildExpr(strExpr);
+        double actual = expr.eval("x = 10; y = 13");
+        double expected = 130;
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void div() {
+        String strExpr = "(x/y)";
+        Expression expr = buildExpr(strExpr);
+        double actual = expr.eval("x = 13; y = 10");
+        double expected = 1.3;
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void complex() {
+        String strExpr = "(3+(((2*x)/y)-z))";
+        Expression expr = buildExpr(strExpr);
+        double actual = expr.eval("x = 15; y = 10; z = 5");
+        double expected = 1;
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void noRequiredVarValue() {
+        String strExpr = "(3+(((2*x)/y)-z))";
+        Expression expr = buildExpr(strExpr);
+        assertThrows(NoSuchElementException.class, () -> expr.eval("x = 15; y = 10"));
+    }
+
+    @Test
+    void noRequiredVarsValues() {
+        String strExpr = "(3+(((2*x)/y)-z))";
+        Expression expr = buildExpr(strExpr);
+        assertThrows(NoSuchElementException.class, () -> expr.eval(""));
+    }
+}
diff --git a/Task_1_3/src/test/java/ru/nsu/sharapov/PrintTest.java b/Task_1_3/src/test/java/ru/nsu/sharapov/PrintTest.java
new file mode 100644
index 0000000..8208025
--- /dev/null
+++ b/Task_1_3/src/test/java/ru/nsu/sharapov/PrintTest.java
@@ -0,0 +1,49 @@
+package ru.nsu.sharapov;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static ru.nsu.sharapov.Parser.buildExpr;
+
+import org.junit.jupiter.api.Test;
+
+public class PrintTest {
+
+    @Test
+    void add() {
+        String expected = "((a+b)+128)";
+        Expression expr = buildExpr(expected);
+        String actual = expr.toString();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void sub() {
+        String expected = "(128-(a-b))";
+        Expression expr = buildExpr(expected);
+        String actual = expr.toString();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mul() {
+        String expected = "(a*(b*128))";
+        Expression expr = buildExpr(expected);
+        String actual = expr.toString();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void div() {
+        String expected = "(b/(a/128))";
+        Expression expr = buildExpr(expected);
+        String actual = expr.toString();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void complex() {
+        String expected = "(((a+b)/(128*c))-8)";
+        Expression expr = buildExpr(expected);
+        String actual = expr.toString();
+        assertEquals(expected, actual);
+    }
+}
diff --git a/Task_1_3/src/test/java/ru/nsu/sharapov/SimplifyTest.java b/Task_1_3/src/test/java/ru/nsu/sharapov/SimplifyTest.java
new file mode 100644
index 0000000..61b4c80
--- /dev/null
+++ b/Task_1_3/src/test/java/ru/nsu/sharapov/SimplifyTest.java
@@ -0,0 +1,80 @@
+package ru.nsu.sharapov;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class SimplifyTest {
+
+    @Test
+    void addZeroRight() {
+        Expression expr = new Add(new Variable("x"), new Number(0));
+        Expression actual = expr.simplify();
+        Expression expected = new Variable("x");
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void addZeroLeft() {
+        Expression expr = new Add(new Number(0), new Variable("x"));
+        Expression actual = expr.simplify();
+        Expression expected = new Variable("x");
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void divZero() {
+        Expression expr = new Div(new Number(0), new Variable("x"));
+        Expression actual = expr.simplify();
+        Expression expected = new Number(0);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void divOne() {
+        Expression expr = new Div(new Variable("x"), new Number(1));
+        Expression actual = expr.simplify();
+        Expression expected = new Variable("x");
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mulZero() {
+        Expression expr = new Mul(new Variable("x"), new Number(0));
+        Expression actual = expr.simplify();
+        Expression expected = new Number(0);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mulOneRight() {
+        Expression expr = new Mul(new Variable("x"), new Number(1));
+        Expression actual = expr.simplify();
+        Expression expected = new Variable("x");
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void mulOneLeft() {
+        Expression expr = new Mul(new Number(1), new Variable("x"));
+        Expression actual = expr.simplify();
+        Expression expected = new Variable("x");
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void subEquals() {
+        Expression expr = new Sub(new Variable("x"), new Variable("x"));
+        Expression actual = expr.simplify();
+        Expression expected = new Number(0);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void noVars() {
+        Expression expr = new Add(new Number(5), new Number(10));
+        Expression actual = expr.simplify();
+        Expression expected = new Number(15);
+        assertEquals(expected, actual);
+    }
+}