# Codeblock 3a
  class Block(nn.Module):
      def __init__(self, 
                   in_channels,            #(1)
                   add_channel=False,      #(2)
                   channel_multiplier=2,   #(3)
                   downsample=False):      #(4)
          super().__init__()
        

        self.add_channel = add_channel
        self.channel_multiplier = channel_multiplier
        self.downsample = downsample
        
        
        if self.add_channel:             #(5)
            out_channels = in_channels*self.channel_multiplier  #(6)
        else:
            out_channels = in_channels   #(7) 
        
        mid_channels = out_channels//2   #(8).
        
        
        if self.downsample:      #(9)
            stride = 2           #(10)
        else:
            stride = 1