diff --git a/lib/core/program.rb b/lib/core/program.rb
index 5860140..1c253be 100644
--- a/lib/core/program.rb
+++ b/lib/core/program.rb
@@ -15,7 +15,6 @@ module Rpl
 
         stack, dictionary = Rpl::Lang::Runner.new.run_input( parsed_input,
                                                              stack, dictionary )
-        # TODO: check that STO actually updates dictionary
 
         [stack, dictionary]
       end
diff --git a/lib/core/store.rb b/lib/core/store.rb
index a3775c5..23caeb5 100644
--- a/lib/core/store.rb
+++ b/lib/core/store.rb
@@ -5,15 +5,113 @@ module Rpl
     module Core
       module_function
 
-      # evaluate (run) a program, or recall a variable. ex: 'my_prog' eval
+      # store a variable. ex: 1 'name' sto
       def sto( stack, dictionary )
-        stack, args = Rpl::Lang::Core.stack_extract( stack, [:any, %i[name]] )
+        stack, args = Rpl::Lang::Core.stack_extract( stack, [%i[name], :any] )
 
-        # TODO
-        dictionary.add( args[1][:value], proc { |stk| Rpl::Lang::Core.eval( stk << args[0][:value], dictionary ) } )
+        dictionary.add_var( args[0][:value][1..-2], # removing surrounding '
+                            proc { |stk, dict, rcl_only = false|
+                              stk << args[1]
+
+                              if rcl_only
+                                [stk, dict]
+                              else
+                                Rpl::Lang::Core.eval( stk, dict )
+                              end
+                            } )
 
         [stack, dictionary]
       end
+
+      # recall a variable. ex: 'name' rcl
+      def rcl( stack, dictionary )
+        stack, args = Rpl::Lang::Core.stack_extract( stack, [%i[name]] )
+
+        word = dictionary[ args[0][:value][1..-2] ]
+
+        stack, dictionary = word.call( stack, dictionary, true ) unless word.nil?
+
+        [stack, dictionary]
+      end
+
+      # delete a variable. ex: 'name' purge
+      def purge( stack, dictionary )
+        stack, args = Rpl::Lang::Core.stack_extract( stack, [%i[name]] )
+
+        dictionary.remove_var( args[0][:value][1..-2] )
+
+        [stack, dictionary]
+      end
+
+      # list all variables
+      def vars( stack, dictionary )
+        # stack << { type: :list,
+        #            value: dictionary.vars.keys.map { |name| { value: name, type: :name } } }
+        stack << { type: :list,
+                   value: dictionary.vars.keys.map { |name| "'#{name}'" } }
+
+        [stack, dictionary]
+      end
+
+      # erase all variables
+      def clusr( stack, dictionary )
+        dictionary.remove_all_vars
+
+        [stack, dictionary]
+      end
+
+      def edit( stack, dictionary )
+        # TODO
+        [stack, dictionary]
+      end
+
+      # add to a stored variable. ex: 1 'name' sto+ 'name' 2 sto+
+      def sto_add( stack, dictionary )
+        stack << { value: '« dup type "name" == « swap » ift over rcl + swap sto »',
+                   type: :program }
+
+        Rpl::Lang::Core.eval( stack, dictionary )
+      end
+
+      # substract to a stored variable. ex: 1 'name' sto- 'name' 2 sto-
+      def sto_subtract( stack, dictionary )
+        stack << { value: '« dup type "name" == « swap » ift over rcl swap - swap sto »',
+                   type: :program }
+
+        Rpl::Lang::Core.eval( stack, dictionary )
+      end
+
+      # multiply a stored variable. ex: 3 'name' sto* 'name' 2 sto*
+      def sto_multiply( stack, dictionary )
+        stack << { value: '« dup type "name" == « swap » ift over rcl * swap sto »',
+                   type: :program }
+
+        Rpl::Lang::Core.eval( stack, dictionary )
+      end
+
+      # divide a stored variable. ex: 3 'name' sto/ 'name' 2 sto/
+      def sto_divide( stack, dictionary )
+        stack << { value: '« dup type "name" == « swap » ift over rcl swap / swap sto »',
+                   type: :program }
+
+        Rpl::Lang::Core.eval( stack, dictionary )
+      end
+
+      # negate a variable. ex: 'name' sneg
+      def sto_negate( stack, dictionary )
+        stack << { value: '« dup rcl -1 * swap sto »',
+                   type: :program }
+
+        Rpl::Lang::Core.eval( stack, dictionary )
+      end
+
+      # inverse a variable. ex: 1 'name' sinv
+      def sto_inverse( stack, dictionary )
+        stack << { value: '« dup rcl 1 swap / swap sto »',
+                   type: :program }
+
+        Rpl::Lang::Core.eval( stack, dictionary )
+      end
     end
   end
 end
diff --git a/lib/dictionary.rb b/lib/dictionary.rb
index 89c7c2f..9fe4ff9 100644
--- a/lib/dictionary.rb
+++ b/lib/dictionary.rb
@@ -3,9 +3,12 @@
 module Rpl
   module Lang
     class Dictionary
+      attr_reader :vars
+
       def initialize
         @parser = Parser.new
         @words = {}
+        @vars = {}
 
         # GENERAL
         add( 'nop',     proc { |stack, dictionary| Rpl::Lang::Core.nop( stack, dictionary ) } )
@@ -133,19 +136,19 @@ module Rpl
         add( 'repeat',  proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # used with while
 
         # STORE
-        add( 'sto',     proc { |stack, dictionary| Rpl::Lang::Core.sto( stack, dictionary ) } ) # store a variable. ex: 1 'name' sto
+        add( 'sto',     proc { |stack, dictionary| Rpl::Lang::Core.sto( stack, dictionary ) } )
         add( '▶',       proc { |stack, dictionary| Rpl::Lang::Core.sto( stack, dictionary ) } ) # alias
-        add( 'rcl',     proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # recall a variable. ex: 'name' rcl
-        add( 'purge',   proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # delete a variable. ex: 'name' purge
-        add( 'vars',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # list all variables
-        add( 'clusr',   proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # erase all variables
+        add( 'rcl',     proc { |stack, dictionary| Rpl::Lang::Core.rcl( stack, dictionary ) } )
+        add( 'purge',   proc { |stack, dictionary| Rpl::Lang::Core.purge( stack, dictionary ) } )
+        add( 'vars',    proc { |stack, dictionary| Rpl::Lang::Core.vars( stack, dictionary ) } )
+        add( 'clusr',   proc { |stack, dictionary| Rpl::Lang::Core.clusr( stack, dictionary ) } )
         add( 'edit',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # edit a variable content
-        add( 'sto+',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # add to a stored variable. ex: 1 'name' sto+ 'name' 2 sto+
-        add( 'sto-',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # substract to a stored variable. ex: 1 'name' sto- 'name' 2 sto-
-        add( 'sto*',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # multiply a stored variable. ex: 3 'name' sto* 'name' 2 sto*
-        add( 'sto/',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # divide a stored variable. ex: 3 'name' sto/ 'name' 2 sto/
-        add( 'sneg',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # negate a variable. ex: 'name' sneg
-        add( 'sinv',    proc { |stack, dictionary| Rpl::Lang::Core.__todo( stack, dictionary ) } ) # inverse a variable. ex: 1 'name' sinv
+        add( 'sto+',    proc { |stack, dictionary| Rpl::Lang::Core.sto_add( stack, dictionary ) } )
+        add( 'sto-',    proc { |stack, dictionary| Rpl::Lang::Core.sto_subtract( stack, dictionary ) } )
+        add( 'sto*',    proc { |stack, dictionary| Rpl::Lang::Core.sto_multiply( stack, dictionary ) } )
+        add( 'sto/',    proc { |stack, dictionary| Rpl::Lang::Core.sto_divide( stack, dictionary ) } )
+        add( 'sneg',    proc { |stack, dictionary| Rpl::Lang::Core.sto_negate( stack, dictionary ) } )
+        add( 'sinv',    proc { |stack, dictionary| Rpl::Lang::Core.sto_inverse( stack, dictionary ) } )
 
         # PROGRAM
         add( 'eval',    proc { |stack, dictionary| Rpl::Lang::Core.eval( stack, dictionary ) } )
@@ -194,11 +197,24 @@ module Rpl
         @words[ name ] = implementation
       end
 
-      def lookup( name )
-        @words[ name ] if @words.include?( name )
+      def add_var( name, implementation )
+        @vars[ name ] = implementation
       end
 
-      # TODO: alias
+      def remove_var( name )
+        @vars.delete( name )
+      end
+
+      def remove_all_vars
+        @vars = {}
+      end
+
+      def []( name )
+        word = @words[ name ]
+        word ||= @vars[ name ]
+
+        word
+      end
     end
   end
 end
diff --git a/lib/runner.rb b/lib/runner.rb
index d020b84..7f064e8 100644
--- a/lib/runner.rb
+++ b/lib/runner.rb
@@ -9,7 +9,7 @@ module Rpl
         input.each do |elt|
           case elt[:type]
           when :word
-            command = dictionary.lookup( elt[:value] )
+            command = dictionary[ elt[:value] ]
 
             if command.nil?
               stack << { type: :name, value: "'#{elt[:value]}'" }
diff --git a/spec/language_program_spec.rb b/spec/language_program_spec.rb
index 4e9b239..a1b0dda 100644
--- a/spec/language_program_spec.rb
+++ b/spec/language_program_spec.rb
@@ -26,11 +26,4 @@ class TestLanguageProgram < Test::Unit::TestCase
                   { value: 4, type: :numeric, base: 10 }],
                  stack
   end
-
-  def test_sto
-    stack, _dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup  »', type: :program },
-                                               { value: "'quatre'", type: :name }], Rpl::Lang::Dictionary.new )
-
-    assert_equal [], stack
-  end
 end
diff --git a/spec/language_store_spec.rb b/spec/language_store_spec.rb
index b3fc65e..446cf13 100644
--- a/spec/language_store_spec.rb
+++ b/spec/language_store_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'test/unit'
@@ -7,10 +6,178 @@ require_relative '../language'
 
 class TestLanguageProgram < Test::Unit::TestCase
   def test_sto
-    stack, _dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup  »', type: :program },
+    stack, dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup * »', type: :program },
+                                              { value: "'quatre'", type: :name }],
+                                             Rpl::Lang::Dictionary.new )
+    assert_equal [], stack
+
+    stack, _dictionary = Rpl::Lang::Core.eval( [{ value: 'quatre', type: :word }],
+                                               dictionary )
+    assert_equal [{ value: 4, type: :numeric, base: 10 }],
+                 stack
+  end
+
+  def test_rcl
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup * »', type: :program },
                                                { value: "'quatre'", type: :name }],
                                               Rpl::Lang::Dictionary.new )
 
-    assert_equal [], stack
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'quatre'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: '« 2 dup * »', type: :program }],
+                 stack
+  end
+
+  def test_purge
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup * »', type: :program },
+                                               { value: "'quatre'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.purge( [{ value: "'quatre'", type: :name }],
+                                                dictionary )
+    assert_equal nil,
+                 dictionary['quatre']
+  end
+
+  def test_vars
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup * »', type: :program },
+                                               { value: "'quatre'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 1, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              dictionary )
+
+    stack, _dictionary = Rpl::Lang::Core.vars( [],
+                                               dictionary )
+    assert_equal [{ value: ["'quatre'", "'un'"], type: :list }],
+                 stack
+  end
+
+  def test_clusr
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: '« 2 dup * »', type: :program },
+                                               { value: "'quatre'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 1, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              dictionary )
+
+    _stack, dictionary = Rpl::Lang::Core.clusr( [],
+                                                dictionary )
+    assert_equal( {},
+                  dictionary.vars )
+  end
+
+  def test_sto_add
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 1, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.sto_add( [{ value: "'un'", type: :name },
+                                                   { value: 3, type: :numeric, base: 10 }],
+                                                  dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 4, type: :numeric, base: 10 }],
+                 stack
+
+    _stack, dictionary = Rpl::Lang::Core.sto_add( [{ value: 3, type: :numeric, base: 10 },
+                                                   { value: "'un'", type: :name }],
+                                                  dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 7, type: :numeric, base: 10 }],
+                 stack
+  end
+
+  def test_sto_subtract
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 1, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.sto_subtract( [{ value: "'un'", type: :name },
+                                                        { value: 3, type: :numeric, base: 10 }],
+                                                       dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: -2, type: :numeric, base: 10 }],
+                 stack
+
+    _stack, dictionary = Rpl::Lang::Core.sto_subtract( [{ value: 3, type: :numeric, base: 10 },
+                                                        { value: "'un'", type: :name }],
+                                                       dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: -5, type: :numeric, base: 10 }],
+                 stack
+  end
+
+  def test_sto_multiply
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 2, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.sto_multiply( [{ value: "'un'", type: :name },
+                                                        { value: 3, type: :numeric, base: 10 }],
+                                                       dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 6, type: :numeric, base: 10 }],
+                 stack
+
+    _stack, dictionary = Rpl::Lang::Core.sto_multiply( [{ value: 3, type: :numeric, base: 10 },
+                                                        { value: "'un'", type: :name }],
+                                                       dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 18, type: :numeric, base: 10 }],
+                 stack
+  end
+
+  def test_sto_divide
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 2, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.sto_divide( [{ value: "'un'", type: :name },
+                                                      { value: 4.0, type: :numeric, base: 10 }],
+                                                     dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 0.5, type: :numeric, base: 10 }],
+                 stack
+
+    _stack, dictionary = Rpl::Lang::Core.sto_divide( [{ value: 5, type: :numeric, base: 10 },
+                                                      { value: "'un'", type: :name }],
+                                                     dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 0.1, type: :numeric, base: 10 }],
+                 stack
+  end
+
+  def test_sto_negate
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 2, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.sto_negate( [{ value: "'un'", type: :name }],
+                                                     dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: -2, type: :numeric, base: 10 }],
+                 stack
+  end
+
+  def test_sto_inverse
+    _stack, dictionary = Rpl::Lang::Core.sto( [{ value: 2, type: :numeric, base: 10 },
+                                               { value: "'un'", type: :name }],
+                                              Rpl::Lang::Dictionary.new )
+
+    _stack, dictionary = Rpl::Lang::Core.sto_inverse( [{ value: "'un'", type: :name }],
+                                                      dictionary )
+    stack, _dictionary = Rpl::Lang::Core.rcl( [{ value: "'un'", type: :name }],
+                                              dictionary )
+    assert_equal [{ value: 0.5, type: :numeric, base: 10 }],
+                 stack
   end
 end