VAR  
  
  a[4]
   
ASSIGN

  init(a) := 0;

  next(a) := 
    case
      flag : inc(a);
      1 : dec(a);
    esac;

SPEC

  AG 
    a = 
      case
        flag : 0;
	1 : 1;
      esac

SPEC
  
  inc(0) = 1
