n = q->avl_link[dir] =
  tree->avl_alloc->libavl_malloc (tree->avl_alloc, sizeof *n);
if (n == NULL)
  return NULL;

tree->avl_count++;
n->avl_data = item;
n->avl_link[0] = n->avl_link[1] = NULL;
n->avl_balance = 0;
if (y == NULL)
  return &n->avl_data;

