# Return the set of all elements `t` that have a direct edge from `element` to `t`.
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["B"].direct_greaters.has_exactly(["C"])
	# ~~~~
	fun direct_greaters: Collection[E]
	do
		return self.dtos
	end