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