      "        root.right = right\n",
      "        root.left.right = invalid\n",
      "        assert_equal(validate_bst(root), False)\n",
      "        print('Success: test_bst_validate')\n",
      "\n",
      "\n",
      "def main():\n",
 
</s> remove     "def __validate_bst__(node, mininum, maximum):\n",
 </s> add     "def _validate_bst(node, mininum, maximum):\n",
    "\n",
      "        root.right = right\n",
      "        root.left.right = invalid\n",
      "        assert_equal(validate_bst(root), False)\n",
    "\n",
      "        print('Success: test_bst_validate')\n",
      "\n",
      "\n",
      "def main():\n",
keep keep add keep keep keep keep
 Polish bst validate challenge and solution (#83)

Update constraints, test cases, tests, algorithm discussion, and code. 
graphs_trees/bst_validate/bst_validate_challenge.ipynb