I was reading Rutten's "Universal coalgebra: a theory of systems" [Theoretical Computer Science 249 (2000) 3-80]. He defines an F-coalgebra or F-system as a pair (S, \alpha_S) where S is a set and \alpha_S: S \rightarrow F(S). But F is free, so where does F come from? An obvious answer would be to redefine F-system as (S,\alpha_S,F). But then the idea came to me that algebras=datatypes and coalgebras=dynamics and therefore a system (really general system) should be the pair (algebra,coalgebra)? Where am I going wrong? -- Dr. D. E. Stevenson, School of Computer Science 315 McAdams Hall, Clemson University 864-656-5880 Be Well. Do Good Works. Stay in Touch. Garrison Keillor [For admin and other information see: http://www.mta.ca/~cat-dist/ ]