If S is a binary predicate, then models neg exists y forall x$[$S$($x$,$y$)$ leftrightarrow neg S$($x$,$ x$)]$ is true.

One may wish to think of the predicate S$($x$,$ y$)$ as representing $"$y shaves z$".$ This viewpoint relates the sentence above to Russell's barber paradoz, which is a fun thing to google and learn about, although it isn't strictly necessary for the problem or the module.