Alfred H. Schatz
Some new local error estimates in negative norms with an application to local a posteriori error estimation.
Int. J. Numer. Anal. Mod., 3 (2006), pp. 371-376. Abstract
Demlow A
Sharply localized pointwise and W-infinity(-1) estimates for finite element methods for quasilinear problems
MATH COMPUT, 76, 260(2007), pp. 1725-1741