# Add the Bucketable event `e` at `at_tick`.
	fun add_at(e: Bucketable[G], at_tick: Int)
	do
		var at_key = key_for_tick(at_tick)

		if at_key == current_bucket_key then
			next_bucket.as(not null).add(e)
		else
			buckets[at_key].add(e)
		end

		e.act_at = at_tick
	end