@techreport{Bornemann1991, author = {Folkmar A. Bornemann}, title = {A Sharpened Condition Number Estimate for the BPX Preconditioner of Elliptic Finite Element Problems on Highly Nonuniform Triangulations.}, institution = {ZIB}, address = {Takustr. 7, 14195 Berlin}, number = {SC-91-09}, language = {eng}, year = {1991} }