A Van Kampen Theorem for Separable Algebras

Andy R. Magid
1973 Proceedings of the American Mathematical Society  
If the commutative ring 5 is the fibre product of Rx and R2 over R, and if R2 maps onto R, then the fundamental group of S is the profinite free product of the fundamental groups of R¡ and R2 with the fundamental group of R amalgamated. Van Kampen's theorem in algebraic topology asserts that, under suitable hypotheses, if Y->X1
doi:10.2307/2039579 fatcat:7x77qnlt5ngtpb3yi46h3hcaxq