Continue with the notation of Example $3\mathrm{.}11.$ Which of the variables x and y is free in thesentence P$($x$,$ y$)?$ Answer the same question about each of the four sentences $($y$)$P$($x$,$ y$),($x$)($y$)$P$($x$,$ y$),($x$)$P$($x$,$ y$),$ and $($y$)($x$)$P$($x$,$ y$)$