On symmetric and twisted-unitary modular units in group rings

Abstract: We study units in group rings of the Hantzsche-Wendt group. We construct a compatible system of non-trivial unitary units over $\mathbb Z/2^n\mathbb Z$ for every $n\ge1$, and ``almost-group'' units over $\mathbb Z/2\mathbb Z$, meaning non-trivial units $u$ with the property that $u-g=u<sup>{-1}-g<sup>{-1}$ for some group element $g$.