Hello, could you provide a source that David Hilbert suffered from dyscalculia? I googled, but I couldn't find any. Furthermore, regarding any such claim, the opposite seems obviously more plausible: 1. Hilbert provided excellent results for Maths in his Abitur examination (Final HIgh school examination/University entrance certificate), where making calculations is more the focus. 2. Hilbert asking a student what the solution to a simple arithmetic expression was cannot be deemed as proof. At the level of mathematical abstraction Hilbert was involved, it makes more sense to me to interpret this anecdote as a joke.

I'd use flipping so as flipping horizontally or vertically (upside down), but in this case I'd call the same as he does (turning).