node counter(res: bool; tick: bool) returns (o: int)
let
  o = if res then 0 else if tick then 1 -> pre o + 1 else 0 -> pre o;
tel

node counter2() returns (b: bool)
var t : async int;
let
  t = async 0 fby async counter(false,true);
  b = counter(false,true) -1 = !t;
tel