Editor's Note: Written contributions relating to material published in the Bulletin will generally appear in the Discussion Section of the Bulletin. Occasionally individuals may be invited to offer discussion for printing with the original paper, article or note. In this instance, Mr. Shepherd, whose paper was referred to by Mr. McKenzie, was invited. His comment and Mr. McKenzie's response appear below. Others may contribute for publication in later issues.
Copyright (c) 1970 R. Shepherd
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