Function perform_among 

pub fn perform_among<'a>(
    suite: &Suite,
    prec: &Precedence,
    state: &Condition,
    action: &Trigger,
    candidates: impl IntoIterator<Item = &'a Expectation>,
) -> Outcome

perform, looking only at candidates: every transition the action might set off must be among them. Searches that perform the same actions over and over work these out once.