code: def concat(self, arrs:Collection[Tensor])->Tensor:
          "Concatenate the `arrs` along the batch dimension."
          return [torch.cat([l[si] for l in arrs], dim=1) for si in range_of(arrs[0])f concat(self, arrs:Collection[Tensor])->Tensor:
          "Concatenate the `arrs` along the batch dimension."
          return [torch.cat([l[si] for l in arrs], dim=1) for si in range_of(arrs[0])]
docs: Concatenate the `arrs` along the batch dimension.