24 Answers votes newest views recent 25Can the Riemann hypothesis be undecidable? 22What is a colimit, really? 17Montague’s Reflection Principle and Compactness Theorem 13“Philosophical” meaning of the Yoneda Lemma 11Why hasn’t mereology suceeded as an alternative to set theory? 10Surreal Numbers and Set Theory 10Geometric Interpretation of Trace 9Arithmetic fixed point theorem 8When a formal power series is a rational function in disguise 5Why should algebraic objects have naturally associated topological spaces? (Formerly: What is a topological space?) 5Tarski’s Theorem and Gödel’s Second Incompleteness Theorem 4existence of a field that has a non surjective ring homomorphism 4 Are all the theorems true? 4Is there a finitely complete category with terminal object but NO subobject classifier? 4What is a complex inner product space “really”? 2Union of a object (a set) in the Elementary Theory of the Category of Sets 2Can we recognize when a category is equivalent to the category of models of a first order theory? 2Hat Problem/Hamming Codes 2Confusion over a point in basic category theory 2wellfounded sets and predecessors 2Proof without words for surface area of a sphere 1Compact Hausdorff and C^*-algebra “objects” in a category. 1What is information-theoretic lower bound? 1Why is the output of an LTI system the convolution of the input funtion and the impulse response?