1. Galileo, “Dialog über die beiden hauptsächlichsten Weltsysteme,” pp. 471-472 (Transl.: Strauss), 1630.
2. Galileo, “Dialogues concerning two new sciences,” p. 239 (Transl.: Crew and De Salvio), 1638.
3. “Lectures on the Calculus of Variations.”;Bliss,1946
4. J. Bernoulli, “Acta Eruditorium,” p. 269. Leipzig, 1696.
5. “The Mathematical Theory of Optimal Processes,”;Pontryagin,1962