Saturday, March 11, 2006

Links to publications 2006

Points of affine categories and additivity
A. Carboni and G. Janelidze, 127-131

A category C is additive if and only if, for every object B of C, the category Pt(C,B) of pointed objects in the comma category (C,B) is canonically equivalent to C. We reformulate the proof of this known result in order to obtain a stronger one that uses not all objects of B of C, but only a conveniently defined generating class S. If C is a variety of universal algebras, then one can take S to be the class consisting of any single free algebra on a non-empty set.

Friday, March 10, 2006

Links to publications 2005

Generic commutative separable algebras and cospans of graphs

R. Rosebrugh, N. Sabadini and R.F.C. Walters

We show that the generic symmetric monoidal category with a commutative separable algebra which has a $\Sigma$-family of actions is the category of cospans of finite $\Sigma$-labelled graphs restricted to finite sets as objects, thus providing a syntax for automata on the alphabet $\Sigma$. We use this result to produce semantic functors for $\Sigma$-automata.

Links to publications 2004

Links to publications 2003

Links to Publications 2002

Feedback, trace and fixed point semantics
P. Katis, N. Sabadini, R.F.C. Walters

We introduce a notion of category with feedback-with-delay, closely related to the notion of traced monoidal category, and show that the Circ construction of [JPAA 115: 141--178, 1997] is the free category with feedback on a symmetric monoidal category. Combining with the Int construction of Joyal-Street-Verity [Math. Proc. Camb.Phil. Soc., 119, 447-468, 1996] we obtain a description of the free compact closed category on a symmetric monoidal category. We thus obtain a categorical analogue of the classical localization of a ring with respect to a multiplicative subset. In this context we define a notion of fixed-point semantics of a category with feedback which is seen to include a variety of classical semantics in computer science.