@article{NUMA_1973__21_132220,
     author = {Gregory M. Nielson},
     title = {Bivariate {Spline} {Functions} and the {Approximation} of {Linear} {Functionals.}},
     journal = {Numerische Mathematik},
     pages = {138--160},
     publisher = {mathdoc},
     volume = {21},
     year = {1973},
     zbl = {0251.41004},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1973__21_132220/}
}