[Ouvrage]
Spline functions: basic theory
/ Principal Schumaker, Larry L..
-Cambridge, New York : Cambridge University Press, 2007. - xv; 582 p.
ISBN 978-0-521-70512-7
[Ouvrage]
N-widths in approximation theory
/ Principal Pinkus, Allan.
-Berlin, Heidelberg, N.Y. : Springer-Verlag, 1985. - 291 p.
ISBN 978-0-387-13638-7