Function held_off_of 

pub fn held_off_of(before: Option<&Press>, state: State) -> i64

What a press of state carries of the press that held before it (Device::held_off): for Reachable, the As usual it found (its stamp), or the one the Reachable it follows carried; else nothing. A gone device’s As usual holds nothing off, so it gives nothing (review of part 3, R-5).