I'm trying to solve the exercise 2.20 from the book "Semantics with Applications" by Nielson & Nielson. The request is the following:
Exercise 2.20 Suppose that (S1;S2,s) =>* (S2,s'). Show that is not necessarily the case that (S1,s) =>* s'.
I suppose that the proof should use induction on the length of the derivation sequence, but I don't even know where to start.
I attach here the table defining the semantics used.