- - which his wife points out that he can step in the same river twice if he goes downstream as fast as the river is flowing.

But, if we follow Helen's post, above, the banks of the river were regarded as an essential part of the river - and they would be different, furhter downstream.

(I agree that one could argue that the bank is not part of the river - but no-one did when it appeared above, so I take that as a justification to take it as given.)