OK I have a problem with this step: <i>[x&#x27;_1,H_1]+[x&#x27;_2,H_2]+[x&#x27;_3,H_3] is equivalent to ∂_1H_1 + ∂_2H_2 + ∂_3H_3 = 0.</i> In the whole paper until the eq. 18 Dyson talks about operators being functions of particle coordinate operators x_k and velocities x&#x27;_k. There is no mention of space coordinates. Suddenly he claims that some operator is equivalent to divergence of a field H that was never mentioned before. It is not clear how does he calculate what ∂_1H_1 is. I do not see how this makes any sense.