A Seifert–Van Kampen theorem describes the fundamental group of a space in terms of the fundamental groups of the constituents of a covering and the conﬁguration of connected components of the covering. Here we provide the combinatorial part of such a theorem for the most general sort of coverings. Thus a Seifert–Van Kampen theorem is reduced to a purely geometric statement of effective descent.
Cite this article
Jakob Stix, A General Seifert–Van Kampen Theorem for Algebraic Fundamental Groups. Publ. Res. Inst. Math. Sci. 42 (2006), no. 3, pp. 763–786