One can notice the similarity between this property and the fact that, if M and N are subspaces of a Banach space where M is closed and N is finite-dimensional, then M + N is also closed.
可以注意到这个性质和如下事实之间的相似性：如果M和N是巴拿赫空间的子空间，其中M是闭的并且N是有限维的，则M+N也是闭的。