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