(2.3) Let $\mathscr{X}$ be a good minimal dlt-model of $X$. We need to make the following technical assumption: the strata of $\mathscr{X}_{k}$ are precisely the log canonical centers of the pair $(\mathscr{X},\mathscr{X}_{k,\mathrm{red}})$ that are contained in $\mathscr{X}_{k}$. By the definition of a dlt-model, every log canonical center of $(\mathscr{X},\mathscr{X}_{k,\mathrm{red}})$ is a stratum. The converse implication is known when $\mathscr{X}$ is defined over an algebraic curve [Ko13, 4.16]. We will prove in Corollary 4.4 that it also holds when $\mathscr{X}_{k}$ is reduced, which is the most important case for our purposes. We expect that the assumption is always satisfied, but the relevant parts of the Minimal Model Program have not been written down for $R$-schemes. In any case, if our technical assumption holds, we can proceed in the following way.