VAR a[2] b[2]
ASSIGN
  init(a) := 0;
  next(a) :=
    case 
      flag1 : inc(a);
      1 : dec(a);
    esac;
  init(b) := 0;
  next(b) :=
    case 
      flag2 : inc(b);
      1 : dec(b);
    esac;
SPEC
AG !(a=0 & b=2)
