Function removeFromSubtree(node, key):
  If node is null:
    ERROR
  If key < node.key:
    node.left = removeFromSubtree(node.left, key)
    return node
  If key > node.key:
    node.right = removeFromSubtree(node.right, key)
    return node
  // key == node.key

  // easy case: leaf node
  If node.left is null and node.right is null:
    delete node
    return null

  // medium cases: node has one child
  If node.left is null:
    new_subtree_root = node.right
    delete node
    return new_subtree_root
  If node.right is null:
    new_subtree_root = node.left
    delete node
    return new_subtree_root

  // hard case: node has two children
  min_key, min_val = findMinInSubtree(node.right)
  new_subtree_root = new BST_Node(min_key, min_val)
  new_subtree_root.left = node.left
  new_subtree_root.right = node.right
  delete node
  new_subtree_root.right = removeFromSubtree(new_subtree_root.right, min_key)
  return new_subtree_root

end Function