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We prove that every set-based functor on the category of classes has a final coalgebra. This result strengthens the final coalgebra theorem announced in the book "Non-well-founded Sets", by the first author. 1 I n t r o d u c t i o n The theorem of this note is an improvement of a result that was first stated, but not proved in its full generality, in(More)
Inÿnite trees form a free completely iterative theory over any given signature—this fact, proved by Elgot, Bloom and Tindell, turns out to be a special case of a much more general categorical result exhibited in the present paper. We prove that whenever an endofunctor H of a category has ÿnal coalgebras for all functors H () + X , then those coalgebras, TX(More)
Rippling is a radically new technique for the automation of mathematical reasoning. It is widely applicable whenever a goal is to be proved from one or more syntactically similar givens. The goal is manipulated to resemble the givens more closely, so that they can be used in its proof. The goal is annotated to indicate which subexpressions are to be moved(More)
Books listed below that are marked with a "t will be reviewed in a future issue. Readers who wish to review books for the journal should write, outlining their qualifications, to: Graeme Hirst, book review editor,ously, we cannot promise the availability ol." books in anyone's exact area of interest. Authors and publishers who wish their books to be(More)
Introduction The original motivation 1 for the work described in this paper was to determine the proof theoretic strength of the type theories implemented in the proof development systems Lego and Coq, Luo and Pollack 92, Barras et al 96]. These type theories combine the impredicative type of propositions 2 , from the calculus of constructions, Coquand 90],(More)