13 Answers votes newest views recent 17What are the most elegant proofs that you have learned from MO? 7Conformal-symplectic geometry ? 6Demystifying complex numbers 6Is there any geometry where the triangle inquality fails? 5Lie group actions and f-relatedness 2Lie group operation and tangent vectors 2Covariant derivative 1Why is the x->x^1/3 atlas on R diffeomorphic with the x->x atlas on R? 1Defining the inverse of the Bott map 1Functional Analysis and its relation to mechanics 0Representations of Pin vs. Representations of Clifford 0Representation of double cover of $U(n)$ on eigenspaces of harmonic oscillator 0when can we lift an action of Lie algebra?