# Cartesian product, over `r` times `self`.
	#
	# See `CartesianCollection` for details.
	#
	# FIXME: Cannot be used if RTA is enabled. So `niti` or `--erasure` only.
	fun product(r: Int): Collection[SequenceRead[E]]
	do
		return new CartesianCollection[E]([self]*r)
	end