exotic 7-sphere

synthetic differential geometry Introductions geometry of physics: coordinate systems, smooth spaces, manifolds, smooth homotopy types, supergeometry Differentials Tangency The magic algebraic facts Theorems Axiomatics Models smooth algebra (-ring) differential equations, variational calculus Chern-Weil theory, ∞-Chern-Weil theory Cartan geometry (super, higher) A topological 7-sphere equipped with an exotic smooth structure is called an exotic 7-sphere. Milnor (1956) gave the first examples of.