new_contents: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  
  import numpy
  
  from chainer import cuda
  from chainer import function
  from chainer.utils import type_check
  
  
  class SquaredDifference(function.Function):
      """Squared difference of input variables."""
  
      def check_type_forward(self, in_types):
          type_check.expect(
              in_types.size() == 2,
              in_types[0].dtype.kind == 'f',
              in_types[0].dtype == in_types[1].dtype,
              in_types[0].shape == in_types[1].shape
          )
  
      def forward(self, inputs):
          xp = cuda.get_array_module(*inputs)
          x1, x2 = inputs
          self.difference = x1 - x2
          y = xp.square(self.difference)
          return y,
  
      def backward(self, inputs, grads):
          x1, x2 = inputs
          gy, = grads
          gx1 = gy * self.difference * 2
          gx2 = gy * self.difference * 2
          return gx1, gx2
  
  def squared_difference(x1, x2):
      """Squared difference of input variables.
  
      Args:
          x1 (~chainer.Variable): Input variables to be compared.
          x2 (~chainer.Variable): Input variables to be compared.
  
      Returns:
          ~chainer.Variable: (x1 - x2)(x1 - x2) element-wise. Output variable. 
      """
      return SquaredDifference()(x1, x2)
  
  
subject: Add squared_difference function