Chebyshev Approximation in ℝn by Curves and Linear Manifolds. - Martin Streng; Wolfgang Wetterling (Curves and Surfaces, 1991)

Parametric Optimization: Singularities, Pathfollowing and Jumps (J. Guddat and F. Guerra Vasquez with H. Th. Jongen). - Wolfgang Wetterling (SIAM Rev., 1993)