code: def forward(
      model: Model[InT, OutT], X1_X2: InT, is_train: bool
  ) -> Tuple[OutT, Callable]:
      X1, X2 = X1_X2
      vec1, bp_vec1 = model.layers[0](X1, is_train)
      vec2, bp_vec2 = model.layers[0](X2, is_train)
      output, bp_output = model.layers[1]((vec1, vec2), is_train)
  
      def finish_update(d_output: OutT) -> InT:
          d_vec1, d_vec2 = bp_output(d_output)
          d_input1 = bp_vec1(d_vec1)
          d_input2 = bp_vec2(d_vec2)
          return (d_input1, d_input2)
  
      return output, finish_update
  
imports: from typing import Callable, Optional, Tuple, TypeVar
  from ..config import registry
  from ..model import Model
  from ..types import ArrayXd
  from ..util import get_width
label_desc: Use image node_id 2 for calling a global function with example usage: forward(model, X1_X2, is_train) and returns: output,  finish_update, d_input1,  d_input2