# Check if the color is free for this holder
	private fun is_color_free(color: Int, holder: H, buckets: Map[H, Set[E]]): Bool do
		if not conflicts.has_key(holder) then return true
		for conflict in conflicts[holder] do
			for bucket in buckets[conflict] do
				if not colors.has_key(bucket) then continue
				if colors[bucket] == color then return false
			end
		end
		return true
	end