The discourse begins with a propositional question. We show how they modify the discourse state.

**Theorem ( c2):**

**Proof ! c2(c2):**
Instantiating the first axiom for the propositional questions, we
get

which, by definition of *c*1, can be written as

Instantiating the axiom for reply we have

and it follows from the two lines above that

which by definition of *c*2 we can write as

Sun Jul 12 14:45:30 PDT 1998