In the paper Attention is all you need, here is Table 1, can someone explain what architecture is referred to in the "Convolution" row and hence describe the other 3 columns in it? The other ones are pretty clear, for example Recurrent, takes $O(d^2)$ operations in one time-step to multiply the hidden state with the weight matrix, and there are $n$ such time-steps, which need to be done sequentially ($O(n)$), also making the information from the first and last tokens in the sentence to travel $O(n)$ steps. For Self-attention, every word in the sentence, attends to every other, so $O(n^2)$ pairs, dot product attention taking $O(d)$ operations. Clearly, the path length is $O(1)$ and there are no sequential operation, all these $O(n^2)$ pairs can be computed independently. The "Convolution" row is not clear to me!