      VAR CONDITION_AT_ENTRANCE : boolean;
      ASSIGN
      init(CONDITION_AT_ENTRANCE) := condition;
      next(CONDITION_AT_ENTRANCE) := case
	!is_fault & next(is_fault) : CONDITION_AT_ENTRANCE;
	is_fault & next(is_fault): CONDITION_AT_ENTRANCE;
	TRUE : next(condition);
      esac;