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 c1, can be written as
Instantiating the axiom for reply we have
and it follows from the two lines above that
which by definition of c2 we can write as
