Counterexample to a conjecture about braces

Abstract

We find an example of a finite solvable group (in fact, a finite $p$-group) without any left brace structure (equiv. which is not an IYB group). Our argument is an improvement of an argument of Rump, using previous work in other areas of Burde, and of Featherstonhaugh, Caranti and Childs, which we relate to brace theory.