16 Answers votes newest views recent 4Open problems in PDEs, dynamical systems, mathematical physics 1on an inequality of Brezis-Lieb 8Does Physics need non-analytic smooth functions? 6Projections in Banach spaces 3Examples of theorems with proofs that have dramatically improved over time 0Does there exist a continuous function of compact support with Fourier transform outside L^1? 1Quasinilpotent example 5On the Paley-Wiener theorem 4Perturbations of an operator that disconnect the spectrum 0Most helpful math resources on the web 2quasinilpotence and finite spectrum 0Theorems that are ‘obvious’ but hard to prove 0Examples of non-rigorous but efficient mathematical methods in physics -1Does a quantitative version of Fredholm theory exist? 2Bounding a spectral gap: what proof techniques exist? 0How is the physical meaning of an irreducible representation justified?