11 Answers votes newest views recent 4How do I make the conceptual transition from multivariable calculus to differential forms? 5Is there any formal foundation to ultrafinitism? 1Is PA consistent? do we know it? 2Which topological spaces admit a nonstandard metric? 2Set theory and Model Theory 10History Question: AUTObiography of Mathematicians 2The set-theoretic multiverse as a (bi)category 1Inconsistent theory with long contradiction 2Why is the concept of topos a “metamorphosis” of the concept of space? 5What is the status of irrational numbers within finitism/ultrafinitism? 1Given a Grothendieck topos, what does its localic groupoid look like?