The category of Hilbert spaces and linear contractions is characterised by elementary categorical properties that do not refer to probabilities, complex numbers, norm, continuity, convexity or dimension.

中文翻译：

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希尔伯特空间范畴和线性收缩的公理

希尔伯特空间和线性收缩的范畴以基本分类属性为特征，这些属性不涉及概率、复数、范数、连续性、凸性或维数。