It's the first symbol referenced for symbols used in proof by contradiction to show contradiction [0]. I know that's not exactly "not" or "disproof" but I think

It's the first symbol referenced for symbols used in proof by contradiction to show contradiction [0]. I know that's not exactly "not" or "disproof" but I think that might be what the poster was getting at. [0] https://en.wikipedia.org/wiki/Contradiction#Symbolic_representation https://en.wikipedia.org/wiki/Contradiction#Symbolic_represe...