P18> ;
--- Output: not_S1_and_not_S2
P18> ;
--- Output: S1_and_S2 S1_and_not_S2 not_S1_and_not_S2
P18> ;
--- Output: S1_and_S2 S1_and_not_S2 not_S1_and_not_S2
P18> ;
--- Output: S1_and_S2 S1_and_not_S2 not_S1_and_not_S2