Three amalgams with remarkable normal subgroup structures

Abstract

We construct three groups $\Lambda_1$, $\Lambda_2$, $\Lambda_3$, which can all be decomposed as amalgamated products $F_9 \ast_{F_{81}} F_{9}$ and have very few normal subgroups of finite or infinite index. Concretely, $\Lambda_1$ is a simple group, $\Lambda_2$ is not simple but has no non-trivial normal subgroup of infinite index, and $\Lambda_3$ is not simple but has no proper subgroup of finite index.