by D. Hull and D.J. Bacon. by D. O. Hall and K. K. Rao. by A. Yariv and J. E. Pearson. by W.B. Gillett and J.E. Moon. by H.S. Hall and S.R. Knight. by D.T.E. Hunt and A.L. Wilson. by J.R. Lucas and P.E. Hodgson. by R.B. Heslop and P.L. Robinson. by J. L. Bell and M. Machover. by J.M. Coulson and J.F. Richardson.