Stallings–Zeeman theorem
In mathematics, the Stallings–Zeeman theorem is a result in algebraic topology, used in the proof of the Poincaré conjecture for dimension greater than or equal to five. It is named after the mathematicians John R. Stallings and Christopher Zeeman. Statement of the theorem
Let M be a finite simplicial complex of dimension dim(M) = m ≥ 5. Suppose that M has the homotopy type of the m-dimensional sphere Sm and that M is locally piecewise linearly homeomorphic to m-dimensional Euclidean space Rm. Then M is homeomorphic to Sm under a map that is piecewise linear except possibly at a single point x. That is, M \ {x} is piecewise linearly homeomorphic to Rm. References
  
  

Theorems in algebraic topology