MAYBE ignored inputs: (COMMENT rules to obtain NNF of first-order formulas ) NRS: [ (0): |- (not (exists [a][]Q)) -> (forall [a](not []Q)), (1): |- (not (forall [a][]Q)) -> (exists [a](not []Q)), (2): |- (not (and <[]P,[]Q>)) -> (or <(not []P),(not []Q)>), (3): |- (not (or <[]P,[]Q>)) -> (and <(not []P),(not []Q)>), (4): |- (not (not []P)) -> []P ] Check confluence by orthogonality abstract skeleton preserving left-linear check proper overlapping a proper overlap exists 0-4 |- < (not (forall [a](not []Q))) <= (not (not (exists [a][]Q))) => (exists [a][]Q) > found proper overlaps result: MAYBE time: 0 msec.