# Is `sub` the greatest lower bound of `sup` considering all `concepts`?
	fun is_lower_neighbour(sub, sup: FormalConcept[O, A], concepts: Set[FormalConcept[O, A]]): Bool
	do
		if sub == sup then return false
		if not sub.is_subconcept(sup) then return false
		for concept in concepts do
			if sub == concept then continue
			if sup == concept then continue
			if not sub.is_subconcept(concept) then continue
			if not concept.is_subconcept(sup) then continue
			return false
		end
		return true
	end