Function by_matrix 

fn by_matrix(ask: &Ask<'_>, events: &[Event], now: Why, later: Why) -> Decision

When a notification comes, by what the matrix says of it at each moment (Attention::decide, its app’s and conversation’s own rows read over its usual one): through now, or held until its first time (first_time), the next event tried when one finds none (its area left aside: nothing waits for good). Why: now or later, or as you chose for this time (Why::Times) when a source’s own cell decides it now.