code: def maxpool(self, input, kernel_size, stride=None):
      return F.max_pool2d(input, kernel_size, stride)
  
imports: import unittest
  import copy
  from collections import OrderedDict
  import numpy
  import torch
  from torch import nn, optim
  from torch.nn import functional
  import higher
label_desc: Use image node_id 3 for calling the _ReferenceNet obj's underlying member method code with example usage: obj.maxpool(input, kernel_size, stride) and returns: F