code: def forward(self, x):
      return self.head(self.trunk(x))
  
imports: from enum import Enum
  from itertools import product
  import tempfile
  import pytest
  import torch
  import torch.multiprocessing
  import torch.nn
  from torch.nn.parallel import DistributedDataParallel
  import torch.optim
  from fairscale.fair_dev.testing.testing import dist_init, objects_are_equal, rmf, skip_if_single_gpu, teardown
  from fairscale.nn.data_parallel import FullyShardedDataParallel
label_desc: Use image node_id 3 for calling the NestedTrunkModel obj's underlying member method code with example usage: obj.forward(x) and returns: self