We obtain some explicit calculations of crossed Q-modules induced from a crossed module over a normal subgroup P of Q. By virtue of theorems of Brown and Higgins, this enables the computation of the homotopy 2-types and second homotopy modules of certain homotopy pushouts of maps of classifying spaces of discrete groups.
Keywords: crossed modules, homotopy 2types, generalized Van Kampen theorem, crossed resolution, Postnikov invariant, classifying spaces of discrete groups.
AMS Classification (1991): 18G10, 20F38, 55P15, 55Q20.
Theory and Applications of Categories, Vol. 2, 1996, No. 1, pp3-16.
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