Direct and Inverse Theorems for Multidimensional Spline Approximation M. MunteanuLarry Schumaker Indiana University Mathematics Journal 1974 text pdf 10.1512/iumj.1974.23.23040 10.1512/iumj.1974.23.23040 en Indiana Univ. Math. J. 23 (1974) 461 - 470 state-of-the-art mathematics http://iumj.org/access/