ﻻ يوجد ملخص باللغة العربية
We provide explicit, simple, geometric formulas for free involutions rho of Euclidean spheres that are not conjugate to the antipodal involution. Therefore the quotient S^n/rho is a manifold that is homotopically equivalent but not diffeomorphic to RP^n. We use these formulas for constructing explicit non-trivial elements in pi_1 Diff(S^5) and pi_1 Diff(S^13) and to provide explicit formulas for non-cancellation phenomena in group actions.
We construct large families of harmonic morphisms which are holomorphic with respect to Hermitian structures by finding heierarchies of Weierstrass-type representations. This enables us to find new examples of complex-valued harmonic morphisms from Euclidean spaces and spheres.
We introduce a combinatorial method to construct indefinite Ricci-flat metrics on nice nilpotent Lie groups. We prove that every nilpotent Lie group of dimension $leq6$, every nice nilpotent Lie group of dimension $leq7$ and every two-step nilpoten
We investigate the problem of when big mapping class groups are generated by involutions. Restricting our attention to the class of self-similar surfaces, which are surfaces with self-similar ends space, as defined by Mann and Rafi, and with 0 or inf
Let k>2. We prove that the cotangent bundles of oriented homotopy (2k-1)-spheres S and S are symplectomorphic only if the classes defined by S and S agree up to sign in the quotient group of oriented homotopy spheres modulo those which bound parallel
Given a combinatorial $(d-1)$-sphere $S$, to construct a combinatorial $d$-sphere $S^{hspace{.2mm}prime}$ containing $S$, one usually needs some more vertices. Here we consider the question whether we can do one such construction without the help of