pat Left (p, q) = p as ref (x, Point p, r, q)
pat Right (p, q) = p as ref (x, l, Point p, q)
pat Child (p, q) = p as ref (x, l, r, q)

fun splay (Left (p, Left (q, r)) = (l3 (p, q, r); splay p)
  | splay (Right (p, Right (q, r)) = (r3 (r, q, p); splay p)
  | splay (Left (p, q)) = (l2 (p, q); splay p)
  | splay (Right (p, q)) = (r2 (q, p); splay p)
  | splay _ = ()