redef fun last_index_in_from(b, from) do
		for i in [0 .. from].step(-1) do if b[i] == self then return i
		return -1
	end

	redef fun last_index_in_from(b, from) do
		if is_empty then return -1
		var lst = self[length - 1]
		var bpos = lst.last_index_in_from(b, from)
		for i in [0 .. length[.step(-1) do
			if self[i] != b[bpos] then return last_index_in_from(b, bpos - 1)
			bpos -= 1
		end
		return bpos
	end