  Sesqui-pushout (SqPO) rewriting is a variant of transformations of graph-like
and other types of structures that fit into the framework of adhesive
categories where deletion in unknown context may be implemented. We provide the
first account of a concurrency theorem for this important type of rewriting,
and we demonstrate the additional mathematical property of a form of
associativity for these theories. Associativity may then be exploited to
construct so-called rule algebras (of SqPO type), based upon which in
particular a universal framework of continuous-time Markov chains for
stochastic SqPO rewriting systems may be realized.
