by G. B. Ansell and J. N. Hawthorne. by R. D. Russell and R. M. Farquhar. by D. O. Hall and K. K. Rao. by J. L. Bell and M. Machover. by N. T. Gill and K. C. Vear. by W. T. Elwell and J. A. F. Gidley. by D. Hull and D.J. Bacon. by E. D. Cashwell and C. J. Everett. by J.G. Semple and G.T. Kneebone. by H. C. Town and R. Colebourne.