by B. R. T. Frost and M. B. Waldron. by J. G. Defares and I. N. Sneddon. by S. R. Cockett and K. A. Hilton. by R. E. D. Bishop and D. C. Johnson. by I. F. Henderson and W. D. Henderson. by V. E. Cosslett and W. C. Nixon. by D.T.E. Hunt and A.L. Wilson. by H. J. Emeleus and J. S. Anderson. by W. G. McLean and E. W. Nelson. by K. J. Binns and P. J. Lawrenson.