[1] V. Pták: 
A rate of convergence. Abhandlungen aus dem mathematischen Seminar Hamburg (in print). 
MR 0537831[3] V. Pták: 
Nondiscrete mathematical induction and iterativę existence proofs. Linear algebгa and its applications 13 (1976), 223-238. 
MR 0394119[4] J. Smital: a personal communication.