ptfl (PtNode n@(x, lv) lt rt) Nothing tgt =
    if x == tgt
        then Just n
        else
            if x < tgt
                then ptfl lt Nothing tgt
                else ptfl rt (Just n) tgt
ptfl (PtNode n@(x, lv) lt rt) Nothing tgt =
    if x == tgt
        then Just n
        else
            if x < tgt
                then ptfl lt Nothing tgt
                else ptfl rt (Just n) tgt
ptfl (PtNode n@(x, lv) lt rt) Nothing tgt =
    if x == tgt
        then Just n
        else
            if x < tgt
                then ptfl lt Nothing tgt
                else ptfl rt (Just n) tgt