By repetitively applying the commutation relation $PX = XP - i$, we can in principle get the X;P-ordered form of $P^k X^k$, where all $X$'s are to the left hand side of $P$'s.
However, after fooling around myself, I have only noted that $P^k X^k = (XP-i)(XP-2i)\cdots(XP-ki)$ and $X^kP^k = XP(XP + i)(XP + 2i)\cdots(XP+(k-1)i)$, which is not I wanted.
Is there a nice procedure to arrive at the X;P-ordered form of $P^k X^k$?
