19 Answers votes newest views recent 14Does every non-empty set admit a group structure (in ZF)? 10Forcing as a tool to prove theorems 2Lower Bounds in Theoretical Computer Science 2Distinct well-orderings of the same set 24Does every set admit a rigid binary relation? (and how is this related to the Axiom of Choice?) (2) 9Uses of bisimulation outside of computer science. 4Singular Cardinals, and A Strange Question. 4Cantor-Bernstein for notions of forcing 4Is it possible for countably closed forcing to collapse $\aleph_2$ to $\aleph_1$ without collapsing the continuum? 10If Q is a subset of the plane of size less than continuum, then does every closed F in Q extend to a closed connected G in the plane with the same trace on Q? (Or is this independent of ZFC?) 11How can an ultrapower of a model of ZFC be “ill-founded” yet still satisfy ZFC? 7Model of ZF + $\neg$C in which Solovay’s Theorem on stationary sets fails? 6Determinacy interchanging the roles of both players 8Background for classic forcing 7Difference between Laver’s and Mathias’s forcing 7Subsets of sequences of natural numbers vs. strategies under ZFC 2a result about Laver property 3A proof for cof(C,M)=cov(M) 5Is $sat(I)$ always a regular cardinal?