Existence and non-existence of skew branes
  Following recent work by Ghomi, Solomon and Tabachnikov, we study geometry and topology of skew branes. A skew brane is a codimension 2 submanifold in affine space such that the tangent spaces at any pair of distinct points are not parallel. We prove that if an oriented closed manifold has a non-zero Euler characteristic $\xi$ then it is not a skew brane; generically, the number of oppositely oriented pairs of parallel tangent spaces is not less than $(\xi^2)/4$. We also construct examples of skew odd-dimensional spheres and skew two-dimensional tori. 
S. Tabachnikov, Yu. Tyurina