Let X,Y be Hilbert space and T:X→Y be a mapping.This paper showed that T was a affine isometry if T preserves 1 and another postive real number , hence partly solved the Aleksandrov problem .%设X和Y是希尔伯特空间,T:X→Y为一映射,证明了若T保1和另外一个实数,则T是一个线性变换,从而部分解决了Aleksandrov问题。
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