what do these lines work for

[share020]

x_pad = tf.concat([x,tf.ones(xs[:-1]+[1])],3) # add channel of ones to distinguish image from padding later on
u_list = [nn.down_shift(nn.down_shifted_conv2d(x_pad, num_filters=nr_filters, filter_size=[2, 3]))] # stream for pixels above
ul_list = [nn.down_shift(nn.down_shifted_conv2d(x_pad, num_filters=nr_filters, filter_size=[1,3])) + nn.right_shift(nn.down_right_shifted_conv2d(x_pad, num_filters=nr_filters, filter_size=[2,1]))]