anchor.diff:        chosen_path = VARIABLE_SET.generate_new_state_variable();
      }
   
  +   :
      (WS)* AF_OPERATOR_KW
         bl_formula[next_state]
      (WS)* R_PAREN
  
positive.code: 
  /** Special Expressions *******************************************************/
  sl_ctl_verifies_operator
     returns [Formula result]:
  
     @init
     {
  
negative.code: ;
  
  bl_af_operator [Variable current_state]
     returns [Formula result]
  
     @init
     {
  