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

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