1. R. E. Langer (Editor), On Numerical Approximation, Univ. of Wisconsin Press, Madison, Wis., 1959, pp. 11–23.
2. L. W. Johnson, Approximation of Vector-Valued Functions, Dissertation, Michigan State Univ., East Lansing, Mich., 1967.
3. Chebyshev approximations of a function and its derivatives;Moursund, D. G.;Math. Comp.,1964