Many reputable sources (I can give as many as you want) describe Da Vinci as a mathematician, but they never mention a single theorem, result, or lemma that he proved. There's the golden ratio spiral, but that's ad hoc nonsense and certainly not what all the writers were thinking of. He used perspective in drawings, but that was already used and hardly counts anyways. Thus I'm wondering whether anyone here happens to know if he actually proved anything. I suspect not, but I'd be arguing against dozens of writers, journalists, and historians and it's impossible to prove a negative.