It is shown that the elements of amalgamated free products in a variety of universal algebras have unique normal forms if the variety is represented by a confluent term rewriting system satisfying some additional requirements for its signature and rules. Applying this fact it is proved that any codescent morphism is effective in such varieties. In particular, this is the case for the variety of Mal'tsev algebras, the varieties of magmas with unit and two-sided inverses, idempotent quasigroups, unipotent quasigroups, left Steiner loops, and right Steiner loops.
"Effective codescent morphisms in the varieties determined by convergent term rewriting systems." Tbilisi Math. J. 9 (1) 49 - 64, June 2016. https://doi.org/10.1515/tmj-2016-0005