Graphical models of program behaviour

I build on the previous lecture by describing the ways in which program execution traces can be analysed into component parts, separated by membranes. Different kinds of membrane are permeable by different kinds of arrows in the graph. As an example, I treat the pi-calculus, together with some of its many variations. Each membrane encloses the execution of a structured component of the program. Again, it would be interesting to discuss some possible biological applications.