Professor Hilbert was unaware that other mathematicians had started calling infinite dimensional inner-product spaces, Hilbert spaces. In fact some of the found

Professor Hilbert was unaware that other mathematicians had started calling infinite dimensional inner-product spaces, Hilbert spaces. In fact some of the foundational results were proven by Von Neumann. The story goes that once Neumann was giving a lecture in Germany on such spaces with Hilbert in attendance. Hilbert had supposedly raised his hands to ask, Dr. von Neumann, I would very much like to know, what after all is a Hilbert space? Hilbert was quite underwhelmed by the definition, "is that all" he remarked.