Presentations of the first homotopy groups of the unitary groups
Abstract
We describe explicit presentations of all stable and the first nonstable homotopy groups of the unitary groups. In particular, for each n >= 2 we supply n homotopic maps that each represent the (n-1)!-th power of a suitable generator of pi2n(U(n)) = Zn!. The product of these n commuting maps is the constant map to the identity matrix.
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