# Return the set of all elements `t` that have an edge from `element` to `t`.
	# Since the POSet is reflexive, element is included in the set.
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["B"].greaters.has_exactly(["B", "C", "D"])
	# ~~~~
	fun greaters: Collection[E]
	do
		return self.tos
	end