-- count the number of top between two tick
node counting (tick:bool; top:bool)
returns (o: int);
var v, o1: int;
let o = if tick then v else 0 -> (pre o) + v;
    v = if top then 1 else 0
tel;

node main (i: int)
returns (o: int);
let
    -- 0 means no `tick` and no `top`
    -- 1 means `tick`
    -- 2 means `top`
    o = counting(i = 1, i = 2)
tel;