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∂AIL Dr. Calvin C. Elgot↓Thomas J. Watson Research Center
↓Yorktown Heights, N.Y. 10598∞

Dear Calvin:

	Thanks for your %2On the Many Facets of Lists%1.  You may be
interested in two related old papers of mine: %2A Basis for a Mathematical
Theory of Computation%1 in Braffort and Hirschberg %2Computer
Programming and Formal Systems%1 North-Holland 1963, and %2Towards
a Mathematical Science of Computation%1 in the Proceedings of the 1962
IFIP congress.  In the former paper, I discuss the formal description
of recursive data structures including lists and S-expressions, and
in the latter, I introduce the idea of %2abstract syntax%1 which is
related - though I don't make the connection.  The idea of recursive
definitions of data structures was re-invented by Hoare in a 1973
paper.  The first paper also discusses the related injections and
projections.

.reg