On the Pontryagin-Steenrod-Wu theorem
  This paper is on homotopy classification of maps of (n+1)-dimensional manifolds into the n-dimensional sphere. For a continuous map f of an (n+1)-manifold into the n-sphere define the degree deg f to be the class dual to f^*[S^n], where [S^n] is the fundamental class. We present a short and direct proof of the following specific case of the Pontryagin-Steenrod-Wu theorem:   Theorem. Let M be a connected orientable closed smooth (n+1)-manifold, n>2. Then the map deg:\pi^n(M)\to H_1(M;Z) is   1-to-1 (i.e., bijective), if the product w_2(M) x r_2 H_2(M;Z) is nonzero, where r_2 is the mod2 reduction;   2-to-1 (i.e., each element of H_1(M;Z) has exactly 2 preimages) - otherwise.   The proof is based on the Pontryagin-Thom construction and a geometric definition of the Stiefel-Whitney classes w_2(M). 
Du\v{s}an Repov\v{s}, Mikhail Skopenkov and Fulvia Spaggiari