diff --git a/lib/risc/instructions/operator_instruction.rb b/lib/risc/instructions/operator_instruction.rb
index 73c4b705..a0d877bb 100644
--- a/lib/risc/instructions/operator_instruction.rb
+++ b/lib/risc/instructions/operator_instruction.rb
@@ -3,33 +3,42 @@ module Risc
   def self.operators
     [:+, :-, :>>, :<<, :*, :&, :|]
   end
-  # Destructive operator instructions on the two registers given
+
+  # Operator instructions on the first two registers given
+  # # Result into the last register
   #
-  # left = left OP right
+  # result = left OP right
   #
   # With OP being the normal logical and mathematical operations provided by
   # cpus. Ie  "+" , "-", ">>", "<<", "*", "&", "|"
   #
+  # Result may be nil, then register is autogenerated
+  #
   class OperatorInstruction < Instruction
-    def initialize( source , operator , left , right )
+    def initialize( source , operator , left , right , result = nil)
       super(source)
       operator = operator.value if operator.is_a?(Sol::Constant)
       @operator = operator
       raise "unsuported operator :#{operator}:#{operator.class}:" unless Risc.operators.include?(operator)
       @left = left
       @right = right
-      raise "Not register #{left}" unless RegisterValue.look_like_reg(left)
-      raise "Not register #{right}" unless RegisterValue.look_like_reg(right)
+      raise "Not register #{left}" unless left.is_a?(RegisterValue)
+      raise "Not register #{right}" unless right.is_a?(RegisterValue)
+      unless result
+        result = RegisterValue.new("op_#{operator}_#{object_id.to_s(16)}".to_sym , :Integer)
+      end
+      raise "Not register #{result}" unless result.is_a?(RegisterValue)
+      @result = result
     end
-    attr_reader :operator, :left , :right
+    attr_reader :operator, :left , :right , :result
 
     def to_s
       class_source "#{left} #{operator} #{right}"
     end
 
   end
-  def self.op( source , operator , left , right )
-    OperatorInstruction.new( source , operator , left , right )
+  def self.op( source , operator , left , right , result = nil)
+    OperatorInstruction.new( source , operator , left , right , result)
   end
 
 end
diff --git a/lib/risc/register_value.rb b/lib/risc/register_value.rb
index 3d1d5664..efce6039 100644
--- a/lib/risc/register_value.rb
+++ b/lib/risc/register_value.rb
@@ -23,6 +23,7 @@ module Risc
       extra = {} unless extra
       @extra = extra
       @symbol = reg
+      raise "not Symbol #{symbol}:#{symbol.class}" unless symbol.is_a?(Symbol)
       raise "Not Hash #{extra}"  unless extra.is_a?(Hash)
       known_type(type)
     end
diff --git a/test/risc/instructions/test_operator_instruction.rb b/test/risc/instructions/test_operator_instruction.rb
new file mode 100644
index 00000000..d9b26453
--- /dev/null
+++ b/test/risc/instructions/test_operator_instruction.rb
@@ -0,0 +1,23 @@
+require_relative "../helper"
+
+module Risc
+  class TestOperatorInstruction < MiniTest::Test
+    def setup
+      Parfait.boot!({})
+      @left = RegisterValue.new(:left , :Integer)
+      @right = RegisterValue.new(:right , :Integer)
+    end
+    def risc(i)
+      @left.op :- , @right
+    end
+    def test_min
+      assert_operator 1 , :- , :left , :right , "op_-_"
+    end
+    def test_reg
+      result = risc(1).result
+      assert_equal RegisterValue , result.class
+      assert_equal "Integer_Type" , result.type.name
+      assert result.symbol.to_s.start_with?("op_-_")
+    end
+  end
+end
diff --git a/test/support/risc_assert.rb b/test/support/risc_assert.rb
index ca5b4347..2cb15b2d 100644
--- a/test/support/risc_assert.rb
+++ b/test/support/risc_assert.rb
@@ -94,7 +94,7 @@ module Minitest
       assert_equal Risc::Branch , branch.class , "Class at:#{branch_i}"
       assert_label branch.label , label_name , "Label  at #{branch_i}"
     end
-    def assert_operator ins_i , op , left , right
+    def assert_operator ins_i , op , left , right , result
       if(ins_i.is_a?(Integer))
         ins = risc(ins_i)
       else
@@ -105,6 +105,7 @@ module Minitest
       assert_equal op , ins.operator
       assert_register :left , left , ins.left , ins_i
       assert_register :right , right , ins.right, ins_i
+      assert_register :result , result , ins.result, ins_i
     end
     def assert_zero ins_i , label
       assert_equal Integer , ins_i.class, "assert_zero #{ins_i}"