... covers and we writeif and implies We say that two events and are two matching events and we write if is the send event and is the receive event In other words, we put if there are twoinstances and ... Ehrig, J. Kreowski, U. Montanari, and G. Rozenberg, editors. Handbook ofGraph Grammars and Computing by Graph Transformation, Vol. 3: Concurrency, Parallelism and Distribution. World Scientific, ... free(F) and Free(F) the sets of first-order and second-ordervariables, respectively, occurring free in F, defined in the obvious way.Given a T-typed graph G, a formula F in and two valuationsand...