“…There are no scale-critical regularity criteria in terms of just one entry of ∇u, but there are a number of results giving subcritical regularity criteria in terms of just one diagonal entry ∂ i u i or one non-diagonal entry ∂ i u j [4,11,17,18,39,41,47,48,50,51,53]. The regularity criteria in terms of one diagonal entry of ∇u are closer to being scale-critical than the regularity criteria in terms of just one non-diagonal entry.…”