Um aus der Definition der Erdös-Zahl eine Schranke von 4 für meine Zahl zu bestimmen, genügen die folgenden Zitate:

1. Anderson, J.M., Erdös, P., Pinkus, A, Shisha, Oved,
   The closed linear span of \(\{x^k-c_k\}_1^{\infty}\)
   J. Approx. Theory 43 (1985), pp. 75--80.
2. Pinkus, A, Braess, D,
   Interpolation by Ridge Functions,
   J. Approx. Theory 73 (1993), pp. 218-236
3. Braess, D, C. Schwab,
   Approximation on simplices with respect to weighted Sobolev norms.
   J. Approx. Theory 103 (2001), No. 2, 329-337.
4. J.M. Melenk, C. Schwab,
   Analytic regularity for a singularly perturbed problem,
   SIAM J. Math. Anal. 30 (1999), 379-400