@article{MZ_1988__197_1_183738,
     author = {K. H\"ollig and C. de Boor},
     title = {Approximation {Power} of {Smooth} {Bivariate} {PP} {Functions.}},
     journal = {Mathematische Zeitschrift},
     pages = {343--364},
     publisher = {mathdoc},
     volume = {197},
     number = {1},
     year = {1988},
     zbl = {0616.41010},
     url = {http://geodesic.mathdoc.fr/item/MZ_1988__197_1_183738/}
}