Mixed identities, hereditarily separated actions and oscillation

Given a topological $G$-space we consider equations with parameters over $G$. In particular we formulate some very general conditions on words with parameters $w(\bar{y},\bar{g})$ over $G$ which guarantee that the inequality $w(\bar{y},\bar{g})\mathrm{\ne }1$ has a solution in $G$. These results are illustrated in some typical situations, in particular standard actions of Thompson’s group $F$ and branch groups are considered. The major results of this paper appeared in some form in Section 2 of the PhD thesis of the second author (avalable at arXiv:1308.6330).