class_docstr: Progressive Neural Network column.
code: def forward(self, x):
      prev_xs, last_x = x[:-1], x[-1]
      hs = self.adapter(prev_xs)
      hs += self.itoh(last_x)
      return hs
  
imports: import torch
  import torch.nn.functional
  from torch import nn
  from avalanche.benchmarks.utils.flat_data import ConstantSequence
  from avalanche.models import MultiTaskModule
  from avalanche.models import MultiHeadClassifier
  from avalanche.benchmarks.scenarios import CLExperience
label_desc: Use image node_id 3 for calling the PNNColumn obj's underlying member method code with example usage: obj.forward(x) and returns: hs