diff --git a/bin/demo b/bin/demo
index 4f0f08a..c08072a 100755
--- a/bin/demo
+++ b/bin/demo
@@ -4,21 +4,27 @@
 require 'bundler/setup'
 require 'ruby_algebra'
 
-puts 'RubyMaple © RubyMaple Creators, 2026. No rights reserved.'
+print "RubyMaple © RubyMaple Creators, 2026. No rights reserved.\nPress Ctrl+D to quit.\n"
 
+interp = RubyAlgebra::Interpreter.new
 loop do
-  puts 'Введите формулу (пустая строка для выхода): '
-  inp = $stdin.gets.chomp
-  exit if inp.empty?
-  begin
-    formula = RubyAlgebra::Parser.parse(inp)
-  rescue StandardError
-    puts 'Ошибка синтаксиса'
-  end
-  puts "Формула: #{formula}"
-  puts "Производная по x: #{formula.diff('x')}"
-  puts "Производная по y: #{formula.diff('y')}"
+  print '> '
+  inp = $stdin.gets
+  break if inp.nil?
 
-  value = formula.evaluate
-  puts "Числовое значение: #{value}" unless value.nil?
+  inp = inp.chomp
+  next if inp.empty?
+
+  begin
+    command = RubyAlgebra::Parser.parse_command(inp)
+  rescue StandardError => e
+    puts "Syntax error: #{e.message}"
+    next
+  end
+  begin
+    puts "< #{interp.execute(command)}"
+  rescue StandardError => e
+    puts "Calculation error: #{e.message}"
+  end
 end
+puts
diff --git a/lib/ruby_algebra.rb b/lib/ruby_algebra.rb
index 2664ef9..d36913d 100644
--- a/lib/ruby_algebra.rb
+++ b/lib/ruby_algebra.rb
@@ -4,3 +4,4 @@ require_relative 'ruby_algebra/version'
 require_relative 'ruby_algebra/command'
 require_relative 'ruby_algebra/polynomial'
 require_relative 'ruby_algebra/parser'
+require_relative 'ruby_algebra/interpreter'
diff --git a/lib/ruby_algebra/command.rb b/lib/ruby_algebra/command.rb
index 3a7c643..0a551d4 100644
--- a/lib/ruby_algebra/command.rb
+++ b/lib/ruby_algebra/command.rb
@@ -3,6 +3,11 @@
 module RubyAlgebra
   # Команда интерпретатора
   class Command
+    attr_reader :type
+
+    def type
+      raise NotImplementedError
+    end
   end
 
   # Команда присвоения
@@ -39,20 +44,29 @@ module RubyAlgebra
       end
       result
     end
+
+    def type
+      :assignment
+    end
   end
 
   # Команда вывода на экран
   class DisplayCommand < Command
-    attr_reader :polynomial
+    attr_reader :item
 
-    def initialize(polynomial)
-      @polynomial = polynomial
+    def initialize(item)
+      @type = :display
+      @item = item
     end
 
     def to_s
       result = "Display command: "
-      result += @polynomial.to_s
+      result += @item.to_s
       result
     end
+
+    def type
+      :display
+    end
   end
 end
diff --git a/lib/ruby_algebra/interpreter.rb b/lib/ruby_algebra/interpreter.rb
new file mode 100644
index 0000000..f8e8098
--- /dev/null
+++ b/lib/ruby_algebra/interpreter.rb
@@ -0,0 +1,70 @@
+module RubyAlgebra
+  class Interpreter
+    def initialize
+      @locals = {}
+    end
+
+    def execute(command)
+      case command.type
+      when :assignment
+        unless command.operand1.is_a?(Polynomial)
+          operand1 = @locals[command.operand1]
+          return "Undeclared polynomial: #{command.operand1}" if operand1.nil?
+        else
+          operand1 = command.operand1
+        end
+
+        unless [:assign, :scale, :diff, :subs].include?(command.operation)
+          operand2 = @locals[command.operand2]
+          return "Undeclared polynomial: #{command.operand2}" if operand2.nil?
+        else
+          operand2 = command.operand2
+        end
+
+        case command.operation
+        when :assign
+          @locals[command.lhs] = operand1
+          return "#{command.lhs} = #{operand1}"
+        when :add
+          result = operand1 + operand2
+          @locals[command.lhs] = result
+          return "#{command.lhs} = #{result}"
+        when :sub
+          result = operand1 - operand2
+          @locals[command.lhs] = result
+          return "#{command.lhs} = #{result}"
+        when :mult, :scale
+          result = operand1 * operand2
+          @locals[command.lhs] = result
+          return "#{command.lhs} = #{result}"
+        when :div
+          result = operand1 / operand2
+          @locals[command.lhs[0]] = result[0]
+          @locals[command.lhs[1]] = result[1]
+          return "Quotient: #{command.lhs[0]} = #{result[0]}, remainder: #{command.lhs[1]} = #{result[1]}"
+        when :diff
+          result = operand1
+          operand2.each do |variable|
+            result = result.diff(variable)
+          end
+          @locals[command.lhs] = result
+          return "#{command.lhs} = #{result}"
+        when :subs
+          result = operand1.evaluate(operand2)
+          @locals[command.lhs] = result
+          return "#{command.lhs} = #{result}"
+        end
+      when :display
+        unless command.item.is_a? Polynomial
+          unless @locals[command.item].nil?
+            return @locals[command.item].to_s
+          else
+            return "Undeclared polynomial: #{command.item}"
+          end
+        else
+          return command.item.to_s
+        end
+      end
+    end
+  end
+end
diff --git a/lib/ruby_algebra/parser.rb b/lib/ruby_algebra/parser.rb
index 5ff60d5..0c8f328 100644
--- a/lib/ruby_algebra/parser.rb
+++ b/lib/ruby_algebra/parser.rb
@@ -118,6 +118,9 @@ module RubyAlgebra
       end
     end
 
+    class TokenizerError < StandardError; end
+    class ParserError < StandardError; end
+
     # Класс для разбора выражений на токены
     class Tokenizer
       attr_reader :lookahead
@@ -135,22 +138,16 @@ module RubyAlgebra
       end
 
       def _next_token
-        puts '_next_token'
-
         loop do
           return EndToken.new unless @i < @expr.length
-          puts "i = #{@i}"
           c = @expr[@i]
-          puts "c = #{c}"
           if c.match?(/\p{Alpha}/)
-            puts 'letter'
             j = @i + 1
             j += 1 while j < @expr.length && @expr[j].match?(/\p{Alnum}/)
             token = IdentifierToken.new(@expr[@i...j])
             @i = j
             return token
           elsif c.match(%r{[+\-*/^():,=]})
-            puts 'operator'
             token = nil
             case c
             when '+'
@@ -179,21 +176,17 @@ module RubyAlgebra
             end
             return token
           elsif c.match?(/\p{Digit}|\./)
-            puts 'digit'
             j = @i + 1
             j += 1 while j < @expr.length && @expr[j].match?(/\p{Digit}|\./)
             s = @expr[@i...j]
             @i = j
-            puts "ssss: #{s}"
             fl = s.count '.'
-            raise StandardError, 'malformed number' if fl > 1
+            raise TokenizerError, 'malformed number' if fl > 1
             return fl.zero? ? NumberToken.new(s.to_i) : NumberToken.new(s.to_f)
           elsif c == ' '
-            puts 'whitespace'
             @i += 1
           else
-            puts 'unknown'
-            @i += 1
+            raise TokenizerError, "unrecognized character '#{c}'"
           end
         end
       end
@@ -217,7 +210,7 @@ module RubyAlgebra
             tokenizer.next_token
             n = tokenizer.next_token
             unless n.type == :paren && n.closing == false
-              raise StandardError, "unexpected token #{n.type}, expected ("
+              raise ParserError, "unexpected token #{n.type}, expected ("
             end
             n = tokenizer.lookahead
             if n.type == :id && !n.variable?
@@ -231,23 +224,23 @@ module RubyAlgebra
               tokenizer.next_token
               n = tokenizer.next_token
               unless n.type == :id && n.variable?
-                raise StandardError, "unexpected token #{n.type}, expected variable"
+                raise ParserError, "unexpected token #{n.type}, expected variable"
               end
               diff_variables << n.symbol
             end
             n = tokenizer.next_token
             unless n.type == :paren && n.closing == true
-              raise StandardError, "unexpected token #{n.type}, expected )"
+              raise ParserError, "unexpected token #{n.type}, expected )"
             end
             unless tokenizer.next_token.type == :end
-              raise StandardError, "unexpected token at the end"
+              raise ParserError, "unexpected token at the end"
             end
             return AssignmentCommand.new(left_hand_side, :diff, target, diff_variables)
           elsif operand1.symbol == 'Subs'
             tokenizer.next_token
             n = tokenizer.next_token
             unless n.type == :paren && n.closing == false
-              raise StandardError, "unexpected token #{n.type}, expected ("
+              raise ParserError, "unexpected token #{n.type}, expected ("
             end
             n = tokenizer.lookahead
             if n.type == :id && !n.variable?
@@ -261,35 +254,35 @@ module RubyAlgebra
               tokenizer.next_token
               n = tokenizer.next_token
               unless n.type == :id && n.variable?
-                raise StandardError, "unexpected token #{n.type}, expected variable"
+                raise ParserError, "unexpected token #{n.type}, expected variable"
               end
               variable = n.symbol
               unless tokenizer.next_token.type == :equals
-                raise StandardError, "unexpected token #{n.type}, expected ="
+                raise ParserError, "unexpected token #{n.type}, expected ="
               end
               n = tokenizer.next_token
               unless n.type == :num
-                raise StandardError, "unexpected token #{n.type}, expected number"
+                raise ParserError, "unexpected token #{n.type}, expected number"
               end
               substitutions[variable] = n.value
             end
             n = tokenizer.next_token
             unless n.type == :paren && n.closing == true
-              raise StandardError, "unexpected token #{n.type}, expected )"
+              raise ParserError, "unexpected token #{n.type}, expected )"
             end
             unless tokenizer.next_token.type == :end
-              raise StandardError, "unexpected token at the end"
+              raise ParserError, "unexpected token at the end"
             end
             return AssignmentCommand.new(left_hand_side, :subs, target, substitutions)
           else
             tokenizer.next_token
             operator = tokenizer.next_token
-            raise StandardError, "unexpected token #{operator.type}, expected +, -, * or /" unless [:plus, :minus, :mult, :div].include?(operator.type)
+            raise ParserError, "unexpected token #{operator.type}, expected +, -, * or /" unless [:plus, :minus, :mult, :div].include?(operator.type)
 
             operand2 = tokenizer.next_token
             unless ([:plus, :minus, :mult].include?(operator.type) && operand2.type == :id && !operand2.variable?) ||
                   ([:mult, :div].include?(operator.type) && operand2.type == :num)
-              raise StandardError, 'unsupported operation or invalid syntax'
+              raise ParserError, 'unsupported operation or invalid syntax'
             end
             if operand2.type == :num
               if operator.type == :mult
@@ -315,49 +308,52 @@ module RubyAlgebra
         n = tokenizer.next_token
         second_lhs = tokenizer.next_token
         unless second_lhs.type == :id && !second_lhs.variable?
-          raise StandardError, "unexpected token #{second_lhs.type}, expected polynomial variable"
+          raise ParserError, "unexpected token #{second_lhs.type}, expected polynomial variable"
         end
         unless tokenizer.next_token.type == :assign
-          raise StandardError, "unexpected token, expected :="
+          raise ParserError, "unexpected token, expected :="
         end
         operand1 = tokenizer.next_token
         unless operand1.type == :id && !operand1.variable?
-          raise StandardError, "unexpected token #{operand1.type}, expected polynomial variable"
+          raise ParserError, "unexpected token #{operand1.type}, expected polynomial variable"
         end
         unless tokenizer.next_token.type == :div
-          raise StandardError, "unexpected token, expected /"
+          raise ParserError, "unexpected token, expected /"
         end
         operand2 = tokenizer.next_token
         unless operand2.type == :id && !operand2.variable?
-          raise StandardError, "unexpected token #{operand2.type}, expected polynomial variable"
+          raise ParserError, "unexpected token #{operand2.type}, expected polynomial variable"
         end
-        return AssignmentCommand.new([left_hand_side, second_lhs.symbol], :div, operand1.symbol)
+        return AssignmentCommand.new([left_hand_side, second_lhs.symbol], :div, operand1.symbol, operand2.symbol)
       elsif tokenizer.lookahead.type == :end
         return DisplayCommand.new(left_hand_side)
       else
-        raise StandardError, "unexpected token #{n.type}, expected ':=' or ','"
+        raise ParserError, "unexpected token #{n.type}, expected ':=' or ','"
       end
     end
 
     def self.parse_polynomial(tokenizer)
-      puts "parse_polynomial <lookahead #{tokenizer.lookahead.type}>"
-      terms = [parse_term(tokenizer)]
+      first_term_negative = false
+      if tokenizer.lookahead.type == :plus || tokenizer.lookahead.type == :minus
+        first_term_negative = tokenizer.lookahead.type == :minus
+        tokenizer.next_token
+      end
+      first_term = parse_term(tokenizer)
+      first_term *= -1 if first_term_negative
+      terms = [first_term]
       while [:plus, :minus].include?(tokenizer.lookahead.type)
         sign = tokenizer.next_token.type == :plus ? +1 : -1
         terms << parse_term(tokenizer) * sign
       end
-      puts 'parse_polynomial end'
       Polynomial.new(terms)
     end
 
     def self.parse_term(tokenizer)
-      puts "parse_term <lookahead #{tokenizer.lookahead.type}>"
       n = tokenizer.lookahead
       unless n.type == :id && n.variable? || n.type == :num
-        raise StandardError, "unexpected token #{n.type}, expected number or variable"
+        raise ParserError, "unexpected token #{n.type}, expected number or variable"
       end
       if n.type == :num
-        puts "eat coeff"
         tokenizer.next_token
         coeff = n.value
         variables = {}
@@ -368,44 +364,34 @@ module RubyAlgebra
       end
       loop do
         n = tokenizer.lookahead
-        puts "<lookahead #{n.type}>"
         unless n.type == :mult || n.type == :id && n.variable?
           break
         end
         v = parse_variable_factor(tokenizer)
         variables[v[0]] = v[1]
       end
-      puts 'parse_term end'
-      pp [coeff, variables]
       Term.new(coeff, variables)
     end
 
     def self.parse_variable_factor(tokenizer)
-      puts "parse_term <lookahead #{tokenizer.lookahead.type}>"
       n = tokenizer.lookahead
       tokenizer.next_token
-      puts 'eat variable'
       if n.type == :mult
         n = tokenizer.next_token
-        puts 'eat *'
       end
       unless n.type == :id && n.variable?
-        raise StandardError, "unexpected token #{n.type}, expected variable"
+        raise ParserError, "unexpected token #{n.type}, expected variable"
       end
       variable = n.symbol
       if tokenizer.lookahead.type == :pow
         tokenizer.next_token
-        puts 'eat ^'
         unless tokenizer.lookahead.type == :num
-          raise StandardError, "unexpected token #{n.type}, expected number"
+          raise ParserError, "unexpected token #{n.type}, expected number"
         end
         power = tokenizer.next_token.value
-        puts 'eat exponent'
       else
         power = 1
       end
-      puts 'parse_variable_factor end'
-      pp [variable, power]
       [variable, power]
     end
   end
diff --git a/lib/ruby_algebra/polynomial.rb b/lib/ruby_algebra/polynomial.rb
index 5d5faa6..7c2fb9e 100644
--- a/lib/ruby_algebra/polynomial.rb
+++ b/lib/ruby_algebra/polynomial.rb
@@ -17,7 +17,7 @@ module RubyAlgebra
 
     def to_s
       if @terms.empty?
-        result = ''
+        result = '0'
       else
         result = @terms[-1].to_s
         i = @terms.length - 2
@@ -37,7 +37,7 @@ module RubyAlgebra
       raise NotImplementedError
     end
 
-    def evaluate(values)
+    def substitute(values)
       result = 0
       @terms.each do |term|
         # ...
@@ -67,6 +67,50 @@ module RubyAlgebra
       end
     end
 
+    def /(other)
+      raise StandardError, "cannot divide by zero" if other.zero?
+      return [Polynomial.new, Polynomial.new] if self.zero?
+
+      # Сначала проверить, что оба многочлена от одной и той же переменной
+      t = if @terms.empty? || @terms[-1].variables.empty? then other.terms[-1] else @terms[-1] end
+      unless t.variables.empty?
+        only_variable = t.variables.keys[0]
+        @terms.each do |term|
+          next if term.variables.empty?
+          unless term.variables.length == 1 && term.variables.keys[0] == only_variable
+            raise StandardError, "cannot divide polynomials with different variables"
+          end
+        end
+        other.terms.each do |term|
+          next if term.variables.empty?
+          unless term.variables.length == 1 && term.variables.keys[0] == only_variable
+            raise StandardError, "cannot divide polynomials with different variables"
+          end
+        end
+      end
+
+      quotient = Polynomial.new
+      remainder = self
+      divisor_power = unless other.terms.last.variables.empty? then other.terms.last.variables.first[1] else 0 end
+      loop do
+        break if remainder.zero?
+
+        dividend_power = unless remainder.terms.last.variables.empty? then remainder.terms.last.variables.first[1] else 0 end
+        break if dividend_power < divisor_power
+
+        result_power = dividend_power - divisor_power
+        result_coeff = remainder.terms.last.coeff.to_f / other.terms.last.coeff
+        if result_power > 0
+          q = Term.new(result_coeff, {only_variable => result_power})
+        else
+          q = Term.new(result_coeff, {})
+        end
+        quotient += q
+        remainder -= other * q
+      end
+      [quotient, remainder]
+    end
+
     def **(other)
       result = Polynomial.new([Term.new(1)])
       other.times do
@@ -91,50 +135,40 @@ module RubyAlgebra
       @terms == other.terms
     end
 
-    def simplify
+    def _simplify
       i = 0
       new_terms = @terms.filter { |t| !t.zero? }
       while i < new_terms.length
         j = i + 1
+        annihilated = false
         while j < new_terms.length
           if new_terms[i].similar_to?(new_terms[j])
             new_terms[i] += new_terms[j]
+            new_terms.delete_at(j)
             if new_terms[i].zero?
               new_terms.delete_at(i)
-              i -= 1
-              j -= 1
+              annihilated = true
+              break
             end
-            new_terms.delete_at(j)
-            j -= 1
+          else
+            j += 1
           end
-          j += 1
         end
-        i += 1
+        i += 1 unless annihilated
       end
-      Polynomial.new(new_terms.sort_by { |t| t.total_power })
+      new_terms.sort_by { |t| t.total_power }
+    end
+
+    def simplify
+      Polynomial.new(_simplify)
     end
 
     def simplify!
-      i = 0
-      new_terms = @terms.filter { |t| !t.zero? }
-      while i < new_terms.length
-        j = i + 1
-        while j < new_terms.length
-          if new_terms[i].similar_to?(new_terms[j])
-            new_terms[i] += new_terms[j]
-            if new_terms[i].zero?
-              new_terms.delete_at(i)
-              i -= 1
-              j -= 1
-            end
-            new_terms.delete_at(j)
-            j -= 1
-          end
-          j += 1
-        end
-        i += 1
-      end
-      @terms = new_terms.sort_by { |t| t.total_power }
+      @terms = _simplify
+    end
+
+    def zero?
+      @terms.all? { |t| t.zero? }
     end
   end
 
@@ -160,7 +194,7 @@ module RubyAlgebra
       raise NotImplementedError
     end
 
-    def evaluate(values)
+    def substitute(values)
       raise NotImplementedError
     end
 
@@ -186,6 +220,11 @@ module RubyAlgebra
       Term.new(@coeff * other.coeff, new_variables)
     end
 
+    def /(other)
+      raise StandardError, "cannot divide by zero" if other.zero?
+
+    end
+
     def +@
       Term.new(@coeff, @variables)
     end
@@ -203,7 +242,13 @@ module RubyAlgebra
     end
 
     def to_s
-      result = @coeff != 1 ? @coeff.to_s : ''
+      if @coeff == 1 && !@variables.empty?
+        result = ''
+      elsif @coeff == -1 && !@variables.empty?
+        result = '-'
+      else
+        result = @coeff.to_s
+      end
       unless @variables.empty?
         first = true
         @variables.each do |var, power|