The Kervaire conjecture was formulated around 1963 after a conversation between Kervaire and Baumslag. It states that adding a generator and then a relator to a non-trivial group always yields a non-trivial group. To this day, the conjecture remains unproven in its most general form; however, it has been shown under certain additional hypotheses, either on the new relator or on the original group. For instance, the result holds for locally indicable groups and for locally residually finite groups. In this talk, I will explain Klyachko’s proof of the conjecture for torsion-free groups, which uses a funny property of the sphere known as the Car Crash Theorem, and van Kampen pictures. I will also discuss how these techniques were generalised by Fenn and Rourke to study equations over torsion-free groups defined by a large class of words (amenable words).
