Completeness of Resolution (cont)
n Ground resolution theorem = if S unsatisfiable,
RC(S) contains empty clause.
n Prove by proving contrapositive:
n i.e., if RC(S) doesn’t contain empty clause, S is
satisfiable
n Do this by constructing a model:
n For each Pi, if there is a clause in RC(S) containing Pi and all
other literals in the clause are false, assign Pi = false
n Otherwise Pi = true
n This assignment of Pi is a model for S.