1. Aarseth, S.: 1970, this issue, p. 20.
2. Bettis, D. G.: 1970,Numer. Math. 14, 421?434.
3. Fehlberg, E.: 1968, NASA TR R-287, also 1969,Computing 4, 93.
4. Heggie, D.: 1970, this issue, p. 35.
5. Henrici, P.:1962,Discrete Variable Methods in Ordinary Differential Equations, John Wiley and Sons.