node updown(on_off : bool) returns (o : bool)
let
  automaton
    state Down
      do o = false until on_off then Up
    state Up
      do o = true until on_off then Down
   end;
tel

node main() returns (o:bool)
var half:bool;
let
  o = updown(half);
  half = true fby not half
tel
