anchor.diff:  
   /** Special Expressions *******************************************************/
   sl_ctl_verifies_operator
  -   returns [Formula result]:
  +   returns [Formula result]
   
      @init
      {
  
positive.code:    {
        /* TODO */
        $result =
           $f1.forAll
           (
              f1_state.in
              (
  
negative.code: ;
  
  bl_eu_operator [Variable current_state]
     returns [Formula result]
  
     @init
     {
  