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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mpool(self, k_height, k_width, d_height=2, d_width=2, mode="VALID", input_layer=None, num_channels_in=None):
 """Construct a max pooling layer."""

        return self._pool("mpool", pooling_layers.max_pooling2d, k_height,
                          k_width, d_height, d_width, mode, input_layer,
                          num_channels_in)