evalast(b(ifteb(ifteb(ifteb(t, f, f), t, t), f, f)));
evalast(n(sc(sc z)));
evalast(n(pd(sc(sc z))));
evalast(n(pd(sc(sc(iften(isz(sc z), z, sc z))))));
evalast(n(sc(iften(isz(sc z), z, sc z))));
evalast(n(pd(pd(sc(sc z)))));