Thisclassictextfocusesonellipticboundaryvalueproblemsindomainswithnonsmoothboundariesandonproblemswithmixedboundaryconditions.Itscontentsareessentialforanunderstandingofthebehaviorofnumericalmethodsforpartialdifferentialequations(PDEs)ontwo-dimensionaldomainswithcorners.