设U,V是Hilbert空间H的两个闭子空间,若存在H的闭子空间L满足L+U=H,L+V=H,且L∩U=L∩V={0},则称L是U和V的公共补,本文获得了两子空间有公共补约一些新的特征,给出了等式H=[U∩(U^⊥+V)](+)[V(+)(U^⊥∩V^⊥)]成立的充分必要条件,完全回答了Groβ提出的问题.
Suppose that U and V are two subspaces of a Hilbert space H If there exists a subspace L such that L + U = H,L +V=H and L∩U = L∩V= {0}, then L is said to be a common complement of U and V. In this paper, some new characteristics of common complements of two subspaces are obtained. Meanwhile, a necessary and sufficient condition for the equation H=[U∩(U^⊥+V)](+)[V(+)(U^⊥∩V^⊥)] to hold is given, which it is a complete answer to Groβ's question.