Maps on the n-dimensional subspaces of a Hilbert space preserving principal angles

摘要

In a former paper we studied transformations on the set of all n-dimensional subspaces of a Hilbert space H which preserve the principal angles. In the case when dim H not equal 2n, we could determine the general form of all such maps. The aim of this paper is to complete our result by considering the problem in the remaining case dim H = 2n.