Activity 2:

Process:

1. Make sure your group is *not* the same as for the first activity. Each group should include at least two members who were not in the same group as for the first activity.

As before:
2. Make sure everyone in your group knows everyone else.
3. On a sheet standard notebook paper, write down the names of all the students who are in your group.
4. Each student should consider the question below individually for about three to five minutes.
5. Discuss each others' ideas as a group for about seven or eight minutes.
6. Have one student write down the *group's* consensus (or majority)
answer to the question on the sheet of paper that has everyone's name
on it. The written answer should be no more than two-thirds of the
page in length; other students may suggest, hopefully minor, changes
in the answer. Give the answer sheet to Neelam.

7. The whole process should take no more than 15-20 minutes.

We introduced the idea of *abstract* parse-tree, as against a concrete parse-tree, the difference being that, in the abstract tree, we dropped some of the terminal nodes that were included in the concrete tree.

This is a two-part question:

a. Give a brief, precise characterization of the terminal nodes that are included in the concrete tree that can be dropped in the abstract tree.

b. Is there any relation between this and the distinction between context-free conditions on the one hand and context-sensitive conditions on the other hand? For example, does this distinction make sense independently of whether we used abstract parse trees or concrete parse trees? Explain briefly.