diff --git a/home/torsten/ruby-x/rubyx/test/slot_machine/instruction/test_slot_definition.rb b/home/torsten/ruby-x/rubyx/test/slot_machine/instruction/test_slot_definition.rb
deleted file mode 100644
index e69de29b..00000000
diff --git a/lib/risc/instructions/load_constant.rb b/lib/risc/instructions/load_constant.rb
index 4a043c6e..572d10fa 100644
--- a/lib/risc/instructions/load_constant.rb
+++ b/lib/risc/instructions/load_constant.rb
@@ -9,7 +9,7 @@ module Risc
       super(source)
       @register = register
       @constant = constant
-      raise "Not Constant #{constant}" if constant.is_a?(SlotMachine::SlotDefinition)
+      raise "Not Constant #{constant}" if constant.is_a?(SlotMachine::Slot)
       raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
     end
     attr_accessor :register , :constant
diff --git a/lib/slot_language/slot_maker.rb b/lib/slot_language/slot_maker.rb
index c922c4f1..98da64de 100644
--- a/lib/slot_language/slot_maker.rb
+++ b/lib/slot_language/slot_maker.rb
@@ -18,7 +18,7 @@ module SlotLanguage
     end
 
     def slot_def(compiler)
-      SlotMachine::SlotDefinition.for(:message , leaps)
+      SlotMachine::Slot.for(:message , leaps)
     end
 
     def to_s
diff --git a/lib/slot_machine/instruction/argument_transfer.rb b/lib/slot_machine/instruction/argument_transfer.rb
index 68575cbc..5d8bd478 100644
--- a/lib/slot_machine/instruction/argument_transfer.rb
+++ b/lib/slot_machine/instruction/argument_transfer.rb
@@ -25,7 +25,7 @@ module SlotMachine
     def initialize( source , receiver,arguments )
       super(source)
       @receiver , @arguments = receiver , arguments
-      raise "Receiver not SlotDefinition #{@receiver}" unless @receiver.is_a?(SlotDefinition)
+      raise "Receiver not Slot #{@receiver}" unless @receiver.is_a?(Slot)
       @arguments.each{|a| raise "args not SlotLoad #{a}" unless a.is_a?(SlotLoad)}
     end
 
diff --git a/lib/slot_machine/instruction/constant_definition.rb b/lib/slot_machine/instruction/constant_slot.rb
similarity index 87%
rename from lib/slot_machine/instruction/constant_definition.rb
rename to lib/slot_machine/instruction/constant_slot.rb
index 3fb4c3c2..e6e7da11 100644
--- a/lib/slot_machine/instruction/constant_definition.rb
+++ b/lib/slot_machine/instruction/constant_slot.rb
@@ -1,14 +1,14 @@
 module SlotMachine
-  class ConstantDefinition < SlotDefinition
+  class ConstantSlot < Slot
     # get the right definition, depending on the object
     def self.for(object , slots)
       case object
       when :message
-        MessageDefinition.new(slots)
+        MessageSlot.new(slots)
       when Constant
-        ConstantDefinition.new(object , slots)
+        ConstantSlot.new(object , slots)
       else
-        SlotDefinition.new(object,slots)
+        Slot.new(object,slots)
       end
     end
 
diff --git a/lib/slot_machine/instruction/message_definition.rb b/lib/slot_machine/instruction/message_slot.rb
similarity index 97%
rename from lib/slot_machine/instruction/message_definition.rb
rename to lib/slot_machine/instruction/message_slot.rb
index cc6f12e0..b83e9428 100644
--- a/lib/slot_machine/instruction/message_definition.rb
+++ b/lib/slot_machine/instruction/message_slot.rb
@@ -1,5 +1,5 @@
 module SlotMachine
-  class MessageDefinition < SlotDefinition
+  class MessageSlot < Slot
 
     def initialize(slots)
       super(:message , slots)
diff --git a/lib/slot_machine/instruction/not_same_check.rb b/lib/slot_machine/instruction/not_same_check.rb
index c2cca3f4..d967a501 100644
--- a/lib/slot_machine/instruction/not_same_check.rb
+++ b/lib/slot_machine/instruction/not_same_check.rb
@@ -3,7 +3,7 @@ module SlotMachine
   # SlotMachine internal check, as the name says to see if two values are not the same
   # In other words, we this checks identity, bit-values, pointers
   #
-  # The values that are compared are defined as SlotDefinitions, ie can be anything
+  # The values that are compared are defined as Slots, ie can be anything
   # available to the machine through frame message or self
   #
   # Acording to SlotMachine::Check logic, we jump to the given label is the values are the same
diff --git a/lib/slot_machine/instruction/object_definition.rb b/lib/slot_machine/instruction/object_slot.rb
similarity index 97%
rename from lib/slot_machine/instruction/object_definition.rb
rename to lib/slot_machine/instruction/object_slot.rb
index 99a47369..8e652106 100644
--- a/lib/slot_machine/instruction/object_definition.rb
+++ b/lib/slot_machine/instruction/object_slot.rb
@@ -1,5 +1,5 @@
 module SlotMachine
-  class ObjectDefinition < SlotDefinition
+  class ObjectSlot < Slot
 
     def initialize( object , slots)
       super(object , slots )
diff --git a/lib/slot_machine/instruction/slot_definition.rb b/lib/slot_machine/instruction/slot.rb
similarity index 83%
rename from lib/slot_machine/instruction/slot_definition.rb
rename to lib/slot_machine/instruction/slot.rb
index dab66bb5..d8536d6e 100644
--- a/lib/slot_machine/instruction/slot_definition.rb
+++ b/lib/slot_machine/instruction/slot.rb
@@ -1,11 +1,11 @@
 module SlotMachine
-  # A SlotDefinition defines a slot. A bit like a variable name but for objects.
+  # A Slot defines a slot. A bit like a variable name but for objects.
   #
   # PS: for the interested: A "development" of Smalltalk was the
   #     prototype based language (read: JavaScript equivalent)
   #     called Self https://en.wikipedia.org/wiki/Self_(programming_language)
   #
-  # SlotDefinitions are the instance names of objects. But since the language is dynamic
+  # Slots are the instance names of objects. But since the language is dynamic
   # what is it that we can say about instance names at runtime?
   # Start with a known object like the Message (in register one), we know all it's
   # variables. But there is a Message in there, and for that we know the instances
@@ -14,16 +14,16 @@ module SlotMachine
   # The definiion is an array of symbols that we can resolve to SlotLoad
   # Instructions. Or in the case of constants to ConstantLoad
   #
-  class SlotDefinition
+  class Slot
     # get the right definition, depending on the object
     def self.for(object , slots)
       case object
       when :message
-        MessageDefinition.new(slots)
+        MessageSlot.new(slots)
       when Constant
-        ConstantDefinition.new(object , slots)
+        ConstantSlot.new(object , slots)
       when Parfait::Object , Risc::Label
-        ObjectDefinition.new(object , slots)
+        ObjectSlot.new(object , slots)
       else
         raise "not supported type #{object}"
       end
diff --git a/lib/slot_machine/instruction/slot_load.rb b/lib/slot_machine/instruction/slot_load.rb
index 9b804570..8734c3ac 100644
--- a/lib/slot_machine/instruction/slot_load.rb
+++ b/lib/slot_machine/instruction/slot_load.rb
@@ -4,9 +4,9 @@ module SlotMachine
   # A Slot is basically an instance variable, but it must be of known type
   #
   # The value loaded (the right hand side) can be a constant (SlotMachine::Constant) or come from
-  #  another Slot (SlotDefinition)
+  #  another Slot (Slot)
   #
-  # The Slot on the left hand side is always a SlotDefinition.
+  # The Slot on the left hand side is always a Slot.
   # The only known object (*) for the left side is the current message, which is a bit like
   # the oo version of a Stack (Stack Register, Frame Pointer, ..)
   # (* off course all class objects are global, and so they are allowed too)
@@ -18,10 +18,10 @@ module SlotMachine
   # From the outside a send is neccessary, both for get and set, (which goes through the method
   # resolution and guarantees the correct method for a type), in other words perfect data hiding.
   #
-  # @left: A SlotDefinition, or an array that can be passed to the constructor of the
-  #        SlotDefinition (see there)
+  # @left: A Slot, or an array that can be passed to the constructor of the
+  #        Slot (see there)
   #
-  # @right: A SlotDefinition with slots or a SlotMachine::Constant
+  # @right: A Slot with slots or a SlotMachine::Constant
   # original_source: optinally another slot_machine instruction that will be passed down
   #                to created  risc instructions. (Because SlotLoad is often used internally)
   class SlotLoad < Instruction
@@ -31,10 +31,10 @@ module SlotMachine
     def initialize(source , left , right, original_source = nil)
       super(source)
       @left , @right = left , right
-      @left = SlotDefinition.for(@left.shift , @left) if @left.is_a? Array
-      @right = SlotDefinition.for(@right.shift , @right) if @right.is_a? Array
-      raise "right not SlotMachine, #{@right.to_s}" unless @right.is_a?( SlotDefinition )
-      raise "left not SlotMachine, #{@left.to_s}" unless @left.is_a?( SlotDefinition )
+      @left = Slot.for(@left.shift , @left) if @left.is_a? Array
+      @right = Slot.for(@right.shift , @right) if @right.is_a? Array
+      raise "right not SlotMachine, #{@right.to_s}" unless @right.is_a?( Slot )
+      raise "left not SlotMachine, #{@left.to_s}" unless @left.is_a?( Slot )
       @original_source = original_source || self
     end
 
@@ -54,7 +54,7 @@ module SlotMachine
   end
 
 end
-require_relative "slot_definition"
-require_relative "message_definition"
-require_relative "constant_definition"
-require_relative "object_definition"
+require_relative "slot"
+require_relative "message_slot"
+require_relative "constant_slot"
+require_relative "object_slot"
diff --git a/lib/slot_machine/instruction/truth_check.rb b/lib/slot_machine/instruction/truth_check.rb
index c2bac6b0..f3cdcfa2 100644
--- a/lib/slot_machine/instruction/truth_check.rb
+++ b/lib/slot_machine/instruction/truth_check.rb
@@ -11,7 +11,7 @@ module SlotMachine
     def initialize(condition , false_jump)
       super(false_jump)
       @condition  = condition
-      raise "condition must be slot_definition #{condition}" unless condition.is_a?(SlotDefinition)
+      raise "condition must be slot_definition #{condition}" unless condition.is_a?(Slot)
     end
 
     def to_s
diff --git a/lib/sol/assignment.rb b/lib/sol/assignment.rb
index 7bb706ea..afc6c7d5 100644
--- a/lib/sol/assignment.rb
+++ b/lib/sol/assignment.rb
@@ -32,7 +32,7 @@ module Sol
     #
     # Derived classes do not implement to_slot, only slot_position
     def to_slot(compiler)
-      to = SlotMachine::SlotDefinition.for(:message , self.slot_position(compiler))
+      to = SlotMachine::Slot.for(:message , self.slot_position(compiler))
       from = @value.to_slot_definition(compiler)
       assign = SlotMachine::SlotLoad.new(self,to,from)
       return assign unless @value.is_a?(CallStatement)
diff --git a/lib/sol/basic_values.rb b/lib/sol/basic_values.rb
index 08f3f0bb..7d3c92e2 100644
--- a/lib/sol/basic_values.rb
+++ b/lib/sol/basic_values.rb
@@ -10,7 +10,7 @@ module Sol
       @value = value
     end
     def to_slot_definition(_)
-      return SlotMachine::SlotDefinition.for(SlotMachine::IntegerConstant.new(@value) , [])
+      return SlotMachine::Slot.for(SlotMachine::IntegerConstant.new(@value) , [])
     end
     def ct_type
       Parfait.object_space.get_type_by_class_name(:Integer)
@@ -38,7 +38,7 @@ module Sol
       Parfait.object_space.get_type_by_class_name(:True)
     end
     def to_slot_definition(_)
-      return SlotMachine::SlotDefinition.for(Parfait.object_space.true_object , [])
+      return SlotMachine::Slot.for(Parfait.object_space.true_object , [])
     end
     def to_s(depth = 0)
       "true"
@@ -50,7 +50,7 @@ module Sol
       Parfait.object_space.get_type_by_class_name(:False)
     end
     def to_slot_definition(_)
-      return SlotMachine::SlotDefinition.for(Parfait.object_space.false_object , [])
+      return SlotMachine::Slot.for(Parfait.object_space.false_object , [])
     end
     def to_s(depth = 0)
       "false"
@@ -62,7 +62,7 @@ module Sol
       Parfait.object_space.get_type_by_class_name(:Nil)
     end
     def to_slot_definition(_)
-      return SlotMachine::SlotDefinition.for(Parfait.object_space.nil_object , [])
+      return SlotMachine::Slot.for(Parfait.object_space.nil_object , [])
     end
     def to_s(depth = 0)
       "nil"
@@ -77,7 +77,7 @@ module Sol
     end
     def to_slot_definition(compiler)
       @my_type = compiler.receiver_type
-      SlotMachine::SlotDefinition.for(:message , [:receiver])
+      SlotMachine::Slot.for(:message , [:receiver])
     end
     def ct_type
       @my_type
@@ -92,7 +92,7 @@ module Sol
       @value = value
     end
     def to_slot_definition(_)
-      return SlotMachine::SlotDefinition.for(SlotMachine::StringConstant.new(@value),[])
+      return SlotMachine::Slot.for(SlotMachine::StringConstant.new(@value),[])
     end
     def ct_type
       Parfait.object_space.get_type_by_class_name(:Word)
diff --git a/lib/sol/call_statement.rb b/lib/sol/call_statement.rb
index cd6904dd..19b523aa 100644
--- a/lib/sol/call_statement.rb
+++ b/lib/sol/call_statement.rb
@@ -11,7 +11,7 @@ module Sol
     # When used as right hand side, this tells what data to move to get the result into
     # a varaible. It is (off course) the return value of the message
     def to_slot_definition(_)
-      SlotMachine::SlotDefinition.for(:message ,[ :return_value])
+      SlotMachine::Slot.for(:message ,[ :return_value])
     end
 
     def to_s(depth = 0)
diff --git a/lib/sol/lambda_expression.rb b/lib/sol/lambda_expression.rb
index fd00c290..10c0ba18 100644
--- a/lib/sol/lambda_expression.rb
+++ b/lib/sol/lambda_expression.rb
@@ -15,7 +15,7 @@ module Sol
     # fact never called)
     def to_slot_definition(compiler)
       compile(compiler) unless @parfait_block
-      return SlotMachine::SlotDefinition.for(SlotMachine::LambdaConstant.new(parfait_block(compiler)) , [])
+      return SlotMachine::Slot.for(SlotMachine::LambdaConstant.new(parfait_block(compiler)) , [])
     end
 
     # create a block, a compiler for it, compile the block and add the compiler(code)
diff --git a/lib/sol/macro_expression.rb b/lib/sol/macro_expression.rb
index 8464089b..f8fd2e04 100644
--- a/lib/sol/macro_expression.rb
+++ b/lib/sol/macro_expression.rb
@@ -15,7 +15,7 @@ module Sol
     # When used as right hand side, this tells what data to move to get the result into
     # a varaible. It is (off course) the return value of the message
     def to_slot_definition(_)
-      SlotMachine::SlotDefinition.for(:message ,[ :return_value])
+      SlotMachine::Slot.for(:message ,[ :return_value])
     end
 
     def to_s(depth = 0)
diff --git a/lib/sol/send_statement.rb b/lib/sol/send_statement.rb
index 40b8a1a8..1cec6f51 100644
--- a/lib/sol/send_statement.rb
+++ b/lib/sol/send_statement.rb
@@ -116,7 +116,7 @@ module Sol
       defi
     end
     def build_condition(ok_label, compiler)
-      cached_type = SlotMachine::SlotDefinition.for(dynamic_call.cache_entry , [:cached_type])
+      cached_type = SlotMachine::Slot.for(dynamic_call.cache_entry , [:cached_type])
       current_type = receiver_type_definition(compiler)
       SlotMachine::NotSameCheck.new(cached_type , current_type, ok_label)
     end
diff --git a/lib/sol/variables.rb b/lib/sol/variables.rb
index 8232c659..57b4cc52 100644
--- a/lib/sol/variables.rb
+++ b/lib/sol/variables.rb
@@ -12,7 +12,7 @@ module Sol
     include Named
     def to_slot_definition(compiler)
       slot_def = compiler.slot_type_for(@name)
-      SlotMachine::SlotDefinition.for(:message , slot_def)
+      SlotMachine::Slot.for(:message , slot_def)
     end
     def to_s(depth = 0)
       name.to_s
@@ -25,7 +25,7 @@ module Sol
   class InstanceVariable < Expression
     include Named
     def to_slot_definition(_)
-      SlotMachine::SlotDefinition.for(:message , [ :receiver , @name] )
+      SlotMachine::Slot.for(:message , [ :receiver , @name] )
     end
     # used to collect type information
     def add_ivar( array )
@@ -52,7 +52,7 @@ module Sol
       get_named_class.single_class.instance_type
     end
     def to_slot_definition(_)
-      return SlotMachine::SlotDefinition.for( get_named_class, [])
+      return SlotMachine::Slot.for( get_named_class, [])
     end
     def get_named_class
       Parfait.object_space.get_class_by_name(self.name)
diff --git a/lib/sol/yield_statement.rb b/lib/sol/yield_statement.rb
index 19e33ffb..d2752a9f 100644
--- a/lib/sol/yield_statement.rb
+++ b/lib/sol/yield_statement.rb
@@ -34,8 +34,8 @@ module Sol
     #      we brace ourselves with the check, and exit (later raise) if . . .
     def method_check(compiler)
       ok_label = SlotMachine::Label.new(self,"method_ok_#{self.object_id}")
-      compile_method = SlotMachine::SlotDefinition.for( compiler.get_method , [])
-      runtime_method = SlotMachine::SlotDefinition.for( :message , [ :method] )
+      compile_method = SlotMachine::Slot.for( compiler.get_method , [])
+      runtime_method = SlotMachine::Slot.for( :message , [ :method] )
       check = SlotMachine::NotSameCheck.new(compile_method , runtime_method, ok_label)
       # TODO? Maybe create slot instructions for this
       #builder = compiler.builder("yield")
diff --git a/test/slot_machine/instruction/test_argument_transfer.rb b/test/slot_machine/instruction/test_argument_transfer.rb
index 4573e7f1..1c171c5f 100644
--- a/test/slot_machine/instruction/test_argument_transfer.rb
+++ b/test/slot_machine/instruction/test_argument_transfer.rb
@@ -3,7 +3,7 @@ require_relative "helper"
 module SlotMachine
   class TestArgumentTransfer < SlotMachineInstructionTest
     def instruction
-      receiver = MessageDefinition.new( [:receiver])
+      receiver = MessageSlot.new( [:receiver])
       arg = SlotLoad.new("test", [:message, :caller] , [:message,:type] )
       ArgumentTransfer.new("" , receiver ,[arg])
     end
diff --git a/test/slot_machine/instruction/test_slot_definition1.rb b/test/slot_machine/instruction/test_constant_slot.rb
similarity index 85%
rename from test/slot_machine/instruction/test_slot_definition1.rb
rename to test/slot_machine/instruction/test_constant_slot.rb
index 5a73c338..eb1d845e 100644
--- a/test/slot_machine/instruction/test_slot_definition1.rb
+++ b/test/slot_machine/instruction/test_constant_slot.rb
@@ -2,11 +2,11 @@ require_relative "helper"
 
 module SlotMachine
 
-  class TestSlotDefinitionConstant < MiniTest::Test
+  class TestSlotConstant < MiniTest::Test
     def setup
       Parfait.boot!(Parfait.default_test_options)
       @compiler = Risc::FakeCompiler.new
-      @definition = SlotDefinition.for(StringConstant.new("hi") , [])
+      @definition = Slot.for(StringConstant.new("hi") , [])
       @register = @definition.to_register(@compiler , InstructionMock.new)
       @instruction = @compiler.instructions.first
     end
@@ -23,11 +23,11 @@ module SlotMachine
       assert_equal "[StringConstant]" , @definition.to_s
     end
   end
-  class TestSlotDefinitionConstantType < MiniTest::Test
+  class TestSlotConstantType < MiniTest::Test
     def setup
       Parfait.boot!(Parfait.default_test_options)
       @compiler = Risc::FakeCompiler.new
-      @definition = SlotDefinition.for(StringConstant.new("hi") , [:type])
+      @definition = Slot.for(StringConstant.new("hi") , [:type])
       @register = @definition.to_register(@compiler , InstructionMock.new)
       @instruction = @compiler.instructions.first
     end
diff --git a/test/slot_machine/instruction/test_slot_definition.rb b/test/slot_machine/instruction/test_message_slot.rb
similarity index 84%
rename from test/slot_machine/instruction/test_slot_definition.rb
rename to test/slot_machine/instruction/test_message_slot.rb
index 0d7b4ff1..cf589079 100644
--- a/test/slot_machine/instruction/test_slot_definition.rb
+++ b/test/slot_machine/instruction/test_message_slot.rb
@@ -1,10 +1,10 @@
 require_relative "helper"
 
 module SlotMachine
-  class TestSlotDefinitionBasics < MiniTest::Test
+  class TestSlotBasics < MiniTest::Test
 
     def slot(slot = :caller)
-      MessageDefinition.new(slot)
+      MessageSlot.new(slot)
     end
     def test_create_ok1
       assert_equal :message , slot.known_object
diff --git a/test/slot_machine/instruction/test_not_same_check.rb b/test/slot_machine/instruction/test_not_same_check.rb
index 646d2f84..bf56251f 100644
--- a/test/slot_machine/instruction/test_not_same_check.rb
+++ b/test/slot_machine/instruction/test_not_same_check.rb
@@ -3,7 +3,7 @@ require_relative "helper"
 module SlotMachine
   class TestNotSameCheck < SlotMachineInstructionTest
     def instruction
-      target = SlotDefinition.for(:message , :caller)
+      target = Slot.for(:message , :caller)
       NotSameCheck.new(target , target , Label.new("ok" , "target"))
     end
     def test_len
diff --git a/test/slot_machine/instruction/test_slot.rb b/test/slot_machine/instruction/test_slot.rb
new file mode 100644
index 00000000..cf589079
--- /dev/null
+++ b/test/slot_machine/instruction/test_slot.rb
@@ -0,0 +1,23 @@
+require_relative "helper"
+
+module SlotMachine
+  class TestSlotBasics < MiniTest::Test
+
+    def slot(slot = :caller)
+      MessageSlot.new(slot)
+    end
+    def test_create_ok1
+      assert_equal :message , slot.known_object
+    end
+    def test_create_ok2
+      assert_equal Array , slot.slots.class
+      assert_equal :caller , slot.slots.first
+    end
+    def test_to_s
+      assert_equal "[message, caller]" , slot.to_s
+    end
+    def test_create_fail_none
+      assert_raises {slot(nil)}
+    end
+  end
+end
diff --git a/test/slot_machine/instruction/test_slot_definition2.rb b/test/slot_machine/instruction/test_slot2.rb
similarity index 88%
rename from test/slot_machine/instruction/test_slot_definition2.rb
rename to test/slot_machine/instruction/test_slot2.rb
index 25e0a2f5..14fe814f 100644
--- a/test/slot_machine/instruction/test_slot_definition2.rb
+++ b/test/slot_machine/instruction/test_slot2.rb
@@ -1,11 +1,11 @@
 require_relative "helper"
 
 module SlotMachine
-  class TestSlotDefinitionKnown1 < MiniTest::Test
+  class TestSlotKnown1 < MiniTest::Test
     def setup
       Parfait.boot!(Parfait.default_test_options)
       @compiler = Risc::FakeCompiler.new
-      @definition = MessageDefinition.new( :caller)
+      @definition = MessageSlot.new( :caller)
       @register = @definition.to_register(@compiler , "fake source")
       @instruction = @compiler.instructions.first
     end
diff --git a/test/slot_machine/instruction/test_slot_definition3.rb b/test/slot_machine/instruction/test_slot_definition3.rb
deleted file mode 100644
index fd930328..00000000
--- a/test/slot_machine/instruction/test_slot_definition3.rb
+++ /dev/null
@@ -1,27 +0,0 @@
-require_relative "helper"
-
-module SlotMachine
-  class TestSlotDefinitionKnown2 < MiniTest::Test
-    def setup
-      Parfait.boot!(Parfait.default_test_options)
-      @compiler = Risc::FakeCompiler.new
-      @definition = MessageDefinition.new( [:caller , :type])
-      @register = @definition.to_register(@compiler , InstructionMock.new)
-    end
-    def test_def_next_class
-      assert_equal Risc::SlotToReg , @compiler.instructions[1].class
-    end
-    def test_def_next_next_class
-      assert_equal NilClass , @compiler.instructions[2].class
-    end
-    def test_def_next_index
-      assert_equal 0 , @compiler.instructions[1].index
-    end
-    def test_def_next_register
-      assert_equal :r1 , @compiler.instructions[1].register.symbol
-    end
-    def test_def_next_array
-      assert_equal :r1 , @compiler.instructions[1].array.symbol
-    end
-  end
-end
diff --git a/test/slot_machine/instruction/test_truth_check.rb b/test/slot_machine/instruction/test_truth_check.rb
index 73c8014a..949c570c 100644
--- a/test/slot_machine/instruction/test_truth_check.rb
+++ b/test/slot_machine/instruction/test_truth_check.rb
@@ -3,7 +3,7 @@ require_relative "helper"
 module SlotMachine
   class TestSameCheck < SlotMachineInstructionTest
     def instruction
-      target = MessageDefinition.new( :caller)
+      target = MessageSlot.new( :caller)
       TruthCheck.new(target , Label.new("ok" , "target"))
     end
     def test_len
diff --git a/test/sol/class_send/test_class_instance.rb b/test/sol/class_send/test_class_instance.rb
index 2a95093e..90b11209 100644
--- a/test/sol/class_send/test_class_instance.rb
+++ b/test/sol/class_send/test_class_instance.rb
@@ -53,11 +53,11 @@ module Sol
       assert_equal SlotLoad,  @ins.class
     end
     def test_left
-      assert_equal MessageDefinition , @ins.left.class
+      assert_equal MessageSlot , @ins.left.class
       assert_equal [:return_value] , @ins.left.slots
     end
     def test_right
-      assert_equal MessageDefinition , @ins.right.class
+      assert_equal MessageSlot , @ins.right.class
       assert_equal [:receiver , :inst] , @ins.right.slots
     end
   end
diff --git a/test/sol/class_send/test_class_send_inherited.rb b/test/sol/class_send/test_class_send_inherited.rb
index 7ba92e83..b8948ad9 100644
--- a/test/sol/class_send/test_class_send_inherited.rb
+++ b/test/sol/class_send/test_class_send_inherited.rb
@@ -31,7 +31,7 @@ module Sol
     def test_receiver
       assert_equal SlotMachine::ArgumentTransfer,  @ins.next(1).class
       assert_equal 0,  @ins.next(1).arguments.length
-      assert_equal ObjectDefinition,  @ins.next(1).receiver.class
+      assert_equal ObjectSlot,  @ins.next(1).receiver.class
       assert_equal Parfait::Class,  @ins.next(1).receiver.known_object.class
       assert_equal :Space,  @ins.next(1).receiver.known_object.name
     end
diff --git a/test/sol/class_send/test_send_class.rb b/test/sol/class_send/test_send_class.rb
index 954e4a3a..20d564f6 100644
--- a/test/sol/class_send/test_send_class.rb
+++ b/test/sol/class_send/test_send_class.rb
@@ -34,12 +34,12 @@ module Sol
       assert_equal MessageSetup , @ins.class , @ins
     end
     def test_receiver
-      assert_equal SlotDefinition,  @ins.next.receiver.class
+      assert_equal Slot,  @ins.next.receiver.class
       assert_equal Parfait::Class,  @ins.next.receiver.known_object.class
       assert_equal :Object ,  @ins.next.receiver.known_object.name
     end
     def test_receiver_move
-      assert_equal ObjectDefinition,  @ins.next.receiver.class
+      assert_equal ObjectSlot,  @ins.next.receiver.class
     end
     def test_receiver
       assert_equal Parfait::Class,  @ins.next.receiver.known_object.class
diff --git a/test/sol/lambdas/test_assign.rb b/test/sol/lambdas/test_assign.rb
index 7ea12f7f..8cb19a26 100644
--- a/test/sol/lambdas/test_assign.rb
+++ b/test/sol/lambdas/test_assign.rb
@@ -73,7 +73,7 @@ module SolBlocks
     def test_assigns_move
       @ins = compile_main_block( "@a = arg")
       assert_equal SlotMachine::SlotLoad , @ins.class , @ins
-      assert_equal SlotMachine::MessageDefinition , @ins.right.class , @ins
+      assert_equal SlotMachine::MessageSlot , @ins.right.class , @ins
     end
   end
 
diff --git a/test/sol/lambdas/test_if_condition.rb b/test/sol/lambdas/test_if_condition.rb
index 3cb46f4c..9c98676a 100644
--- a/test/sol/lambdas/test_if_condition.rb
+++ b/test/sol/lambdas/test_if_condition.rb
@@ -12,7 +12,7 @@ module SolBlocks
       assert_equal TruthCheck , @ins.next(3).class
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.next(3).condition.class , @ins
+      assert_equal MessageSlot , @ins.next(3).condition.class , @ins
     end
     def test_simple_call
       assert_equal SimpleCall , @ins.next(2).class
diff --git a/test/sol/lambdas/test_while_simple.rb b/test/sol/lambdas/test_while_simple.rb
index 4ed903cf..5c2ceab4 100644
--- a/test/sol/lambdas/test_while_simple.rb
+++ b/test/sol/lambdas/test_while_simple.rb
@@ -15,7 +15,7 @@ module SolBlocks
       assert_equal TruthCheck , @ins.next.class , @ins
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.next.condition.class , @ins
+      assert_equal MessageSlot , @ins.next.condition.class , @ins
     end
     def test_array
       check_array [Label, TruthCheck, SlotLoad, Jump, Label,
diff --git a/test/sol/send/test_send_self.rb b/test/sol/send/test_send_self.rb
index e060a17a..d8f74a15 100644
--- a/test/sol/send/test_send_self.rb
+++ b/test/sol/send/test_send_self.rb
@@ -8,7 +8,7 @@ module Sol
       "self.get_internal_word(0);return"
     end
     def test_receiver
-      assert_equal MessageDefinition,  @ins.next.receiver.class
+      assert_equal MessageSlot,  @ins.next.receiver.class
     end
     def test_arg_one
       assert_equal SlotLoad,  @ins.next(1).arguments[0].class
@@ -23,7 +23,7 @@ module Sol
       assert_equal :get_internal_word,  @ins.next(2).method.name
     end
     def test_receiver_move
-      assert_equal MessageDefinition,  @ins.next.receiver.class
+      assert_equal MessageSlot,  @ins.next.receiver.class
     end
 
   end
diff --git a/test/sol/send/test_send_simple.rb b/test/sol/send/test_send_simple.rb
index c69c8986..1692a31d 100644
--- a/test/sol/send/test_send_simple.rb
+++ b/test/sol/send/test_send_simple.rb
@@ -14,7 +14,7 @@ module Sol
       assert_equal :div4,  @ins.next(2).method.name
     end
     def test_receiver_move
-      assert_equal ConstantDefinition,  @ins.next.receiver.class
+      assert_equal ConstantSlot,  @ins.next.receiver.class
     end
 
   end
diff --git a/test/sol/send/test_send_simple_args.rb b/test/sol/send/test_send_simple_args.rb
index 0bf1b3cb..aad09857 100644
--- a/test/sol/send/test_send_simple_args.rb
+++ b/test/sol/send/test_send_simple_args.rb
@@ -24,7 +24,7 @@ module Sol
                   Label, ReturnSequence , Label] , @ins
     end
     def test_receiver_move
-      assert_equal ConstantDefinition,  @ins.next.receiver.class
+      assert_equal ConstantSlot,  @ins.next.receiver.class
     end
 
   end
diff --git a/test/sol/test_assignment.rb b/test/sol/test_assignment.rb
index 4341ab1f..fac1d5af 100644
--- a/test/sol/test_assignment.rb
+++ b/test/sol/test_assignment.rb
@@ -79,7 +79,7 @@ module Sol
       @compiler = compile_main( "@a = arg;return")
       @ins = @compiler.slot_instructions.next
       assert_equal SlotMachine::SlotLoad , @ins.class , @ins
-      assert_equal SlotMachine::MessageDefinition , @ins.right.class , @ins
+      assert_equal SlotMachine::MessageSlot , @ins.right.class , @ins
     end
   end
 
diff --git a/test/sol/test_class_expression2.rb b/test/sol/test_class_expression2.rb
index 8af2c6ef..7d27c14d 100644
--- a/test/sol/test_class_expression2.rb
+++ b/test/sol/test_class_expression2.rb
@@ -18,7 +18,7 @@ module Sol
       assert_equal TruthCheck , @ins.next.class , @ins
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.next.condition.class , @ins
+      assert_equal MessageSlot , @ins.next.condition.class , @ins
     end
     def test_label_after_check
       assert_equal Label , @ins.next(2).class , @ins
diff --git a/test/sol/test_if_no_else.rb b/test/sol/test_if_no_else.rb
index fa35ad93..a28c7091 100644
--- a/test/sol/test_if_no_else.rb
+++ b/test/sol/test_if_no_else.rb
@@ -14,7 +14,7 @@ module Sol
       assert_equal TruthCheck , @ins.class , @ins
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.condition.class , @ins
+      assert_equal MessageSlot , @ins.condition.class , @ins
     end
     def test_label_after_check
       assert_equal Label , @ins.next.class , @ins
diff --git a/test/sol/test_if_no_if.rb b/test/sol/test_if_no_if.rb
index f4a81725..edbf5199 100644
--- a/test/sol/test_if_no_if.rb
+++ b/test/sol/test_if_no_if.rb
@@ -14,7 +14,7 @@ module Sol
       assert_equal TruthCheck , @ins.class , @ins
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.condition.class , @ins
+      assert_equal MessageSlot , @ins.condition.class , @ins
     end
     def test_label_after_check
       assert_equal Label , @ins.next.class , @ins
diff --git a/test/sol/test_if_simple.rb b/test/sol/test_if_simple.rb
index 777244ba..fef41289 100644
--- a/test/sol/test_if_simple.rb
+++ b/test/sol/test_if_simple.rb
@@ -14,7 +14,7 @@ module Sol
       assert_equal TruthCheck , @ins.class , @ins
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.condition.class , @ins
+      assert_equal MessageSlot , @ins.condition.class , @ins
     end
     def test_label_after_check
       assert_equal Label , @ins.next.class , @ins
diff --git a/test/sol/test_if_statement.rb b/test/sol/test_if_statement.rb
index 36e41d4d..a66e255d 100644
--- a/test/sol/test_if_statement.rb
+++ b/test/sol/test_if_statement.rb
@@ -13,7 +13,7 @@ module Sol
       assert_equal TruthCheck , @ins.next(3).class
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.next(3).condition.class , @ins
+      assert_equal MessageSlot , @ins.next(3).condition.class , @ins
     end
     def test_hoisted_call
       assert_equal SimpleCall , @ins.next(2).class
diff --git a/test/sol/test_while_statement.rb b/test/sol/test_while_statement.rb
index bd6fa679..39b56972 100644
--- a/test/sol/test_while_statement.rb
+++ b/test/sol/test_while_statement.rb
@@ -16,7 +16,7 @@ module Sol
       assert_equal TruthCheck , @ins.next.class , @ins
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.next.condition.class , @ins
+      assert_equal MessageSlot , @ins.next.condition.class , @ins
     end
     def test_array
       check_array [Label, TruthCheck, SlotLoad, Jump, Label ,
diff --git a/test/sol/test_while_statement1.rb b/test/sol/test_while_statement1.rb
index 4bf73a8e..237d009c 100644
--- a/test/sol/test_while_statement1.rb
+++ b/test/sol/test_while_statement1.rb
@@ -14,7 +14,7 @@ module Sol
       assert_equal TruthCheck , @ins.next(4).class
     end
     def test_condition_is_slot
-      assert_equal MessageDefinition , @ins.next(4).condition.class , @ins
+      assert_equal MessageSlot , @ins.next(4).condition.class , @ins
     end
     def test_hoisetd
       jump = @ins.next(8)
diff --git a/test/sol/test_yield_statement.rb b/test/sol/test_yield_statement.rb
index c6ab8245..55e2519a 100644
--- a/test/sol/test_yield_statement.rb
+++ b/test/sol/test_yield_statement.rb
@@ -28,13 +28,13 @@ module Sol
       assert_equal [:next_message, :arg1], left.slots
     end
     def test_check_left
-      assert_equal ObjectDefinition, @ins.left.class
+      assert_equal ObjectSlot, @ins.left.class
       assert_equal Parfait::CallableMethod, @ins.left.known_object.class
       assert_equal :main, @ins.left.known_object.name
       assert @ins.left.slots.empty?
     end
     def test_check_right
-      assert_equal MessageDefinition, @ins.right.class
+      assert_equal MessageSlot, @ins.right.class
       assert_equal :message, @ins.right.known_object
       assert_equal [:method] , @ins.right.slots
     end