Submission date: 12 March 2017

Abstract:

We introduce a combinatorial criterion for verifying whether a formula is not the conjunction of an equation and a co-equation. Using this, we give a transparent proof for the nonequationality of the free group, which was originally proved by Sela. Furthermore, we extend this result to arbitrary free products of groups (except Z_2 * Z_2), providing an abundance of new stable nonequational theories.

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Full text arXiv 1703.04169: pdf, ps.