@Article{ Beuchler.Schoberl:2005, author = {Beuchler, S. and Sch{\"o}berl, J.}, title = {Optimal extensions on tensor-product meshes}, journal = {Appl. Numer. Math.}, fjournal = {Applied Numerical Mathematics. An IMACS Journal}, volume = {54}, year = {2005}, number = {3-4}, pages = {391--405} }