D. Hong,
On optimal order of approximation from bivariate spline spaces ,
In " Proceedings of the Sixth International Colloquium on
Numerical Analysis and Computers with Applications" (D.D. Bainov Ed.),
pp.219-226, VSP, International Sciences
Publishers, Utrecht,
The Netherlands, 1998. CMP 1 644 943 (99:01), MR 99d:
00026.