f (Ps (Ps (Ps (Ps (Ps (Ps P0))))))
f ⌞P 6⌟
@f 6 ⌞@P ⌞true⌟ 6⌟
@f 6 (@Ps 5 (@Ps 4 (@Ps 3 (@Ps 2 (@Ps 1 (@Ps 0 P0))))))