1. M. W. Nirenberg, this series, Vol. 6, p. 17.
2. L. M. Gold and M. Schweiger, this series, Vol. 20, p. 537.
3. S. M. Heywood and A. W. Rourke, this series, Vol. 30, p. 669.
4. A. Marcus, D. Efron, and D. Weeks, this series, Vol. 30, p. 749.
5. W. C. Merrick, this series, Vol. 101, p. 606.