We present a categorical formulation
of the rewriting of possibly cyclic term graphs, based on a
variation of algebraic 2-theories. We show that
this presentation is equivalent to the well-accepted
operational definition proposed by Barendregt et al. – but
for the
case of circular redexes , for which we propose (and
justify formally) a different treatment.
The categorical framework allows us to model in a concise way
also automatic garbage collection
and rules
for sharing/unsharing and folding/unfolding of structures,
and to relate
term graph rewriting to other rewriting formalisms.
