[1] V. Pták: 
Nondiscrete mathematical induction and iterative existence proofs. Lin. Alg. Appl. 13 (1976), pp. 223-230. 
MR 0394119[3] V. Pták: 
What should be a rate of convergence?. RAIRO-Anal. Math. 11 (1977), pp. 279-286. 
MR 0474799[4] V. Pták: 
A rate of convergence. Num. Anal. & Opt. 1 (1979), 255-271. 
MR 0537831