# History of Poincare conjecture in higher dimension [closed]

As far as I know, when Poincare formulated his well known conjecture, the original statement was the follwoing: if a closed manifold has the same homology groups as the sphere it is homoeomorphic to the sphere. Later he found a counterexample for such a statement and reformulated his problem replacing homology groups with the first homotopy group. Later Poincare conjecture was generalized to the higher dimensions. The formulation is the following: if the manifold is homotopy equivalent to the sphere than it is homeomorphic to the sphere. The formulation is therefore different as in dimension $3$. So it suggest that there are simply connected manifolds which are not homeomorphic to sphere. My question is then the following:
Question 1 Was it (the current formulation) the original formulation of generalized Poincare conjecture? Or maybe counterexamples were constructed later and people figured out that the statement of higher dimensional Poincare conjecture should be different?

## closed as unclear what you're asking by HJRW, Sam Nead, Oscar Randal-Williams, Neil Strickland, Noah SchweberFeb 13 '15 at 23:31

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• In dimension $3$, a closed manifold which is simply connected is an integral homology sphere, and in all dimensions, a closed manifold which is simply connected and also an integral homology sphere is homotopy equivalent to a sphere. So the formulation is not so different. – Qiaochu Yuan Feb 12 '15 at 22:45
• "It suggest that there are simply connected manifolds which are not homeomorphic to sphere." $S^2 \times S^2$ is a simple example. – Douglas Zare Feb 12 '15 at 23:48
• I think it goes back to the Witold Hurewicz's theorem. – Włodzimierz Holsztyński Feb 13 '15 at 0:13
• This question is very unclear. Your 'original' statement of the Poincare Conjecture makes no mention of dimension, but you then write 'Later Poincare conjecture was generalized to the higher dimensions.' Since it is unclear what you are asking, I'm voting to close. (Also, as has been pointed out, in the light of Hurewicz's theorem, the generalization to higher dimensions is obvious.) – HJRW Feb 13 '15 at 10:09