Triviality of fundamental groups of spheres of dimension greater than 1 is proven, [17]
@article{bwmeta1.element.doi-10_2478_v10037-012-0013-1, author = {Marco Riccardi and Artur Korni\l owicz}, title = {Fundamental Group of n-sphere for n $\geq$ 2}, journal = {Formalized Mathematics}, volume = {20}, year = {2012}, pages = {97-104}, zbl = {1276.57004}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.doi-10_2478_v10037-012-0013-1} }
Marco Riccardi; Artur Korniłowicz. Fundamental Group of n-sphere for n ≥ 2. Formalized Mathematics, Tome 20 (2012) pp. 97-104. http://gdmltest.u-ga.fr/item/bwmeta1.element.doi-10_2478_v10037-012-0013-1/
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