fold and unfold

[Graham Hutton]

Dear all,

The following new paper may be of interest to some readers of this group:

   	          When is a Function a Fold or an Unfold?

	   Jeremy Gibbons, Graham Hutton, and Thorsten Altenkirch

		   http://www.cs.nott.ac.uk/~gmh/when.pdf
		   http://www.cs.nott.ac.uk/~gmh/when.ps

   We give a necessary and  sufficient condition for when a set-theoretic
   function can be written using  the recursion operator fold, and a dual
   condition  for  the recursion  operator  unfold.   The conditions  are
   simple, practically useful, and generic in the underlying datatype.
   
   (To appear  in the  Proceedings of the  4th International  Workshop on
   Coalgebraic Methods in Computer Science, Genova, Italy, April 2001.)

Best wishes,

Graham

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| Dr Graham Hutton                     Email : gmh@cs.nott.ac.uk              |
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