**3.** The sets of strings produced by G1 and G2, ignoring phi, are
identical. The difference between the grammars is that the trees produced
by G1 are right branching while the trees produced by G2 are left
branching. In G1, at every level of the tree the node that branches
to extend the tree is the right sister while in G2, it is the left sister.

In the terminology of mathematical linguistics (automata theory), these grammars are simple examples of regular or finite state grammars.