let A be QC-alphabet ; :: thesis: for p being Element of CQC-WFF A holds (('not' p) => ('not' (VERUM A))) => p in TAUT A
let p be Element of CQC-WFF A; :: thesis: (('not' p) => ('not' (VERUM A))) => p in TAUT A
( ('not' p) => (('not' (VERUM A)) => p) in TAUT A & (('not' p) => (('not' (VERUM A)) => p)) => ((('not' p) => ('not' (VERUM A))) => (('not' p) => p)) in TAUT A ) by Th11, Th12, Th13;
then A1: (('not' p) => ('not' (VERUM A))) => (('not' p) => p) in TAUT A by CQC_THE1:46;
(('not' p) => p) => p in TAUT A by CQC_THE1:42;
hence (('not' p) => ('not' (VERUM A))) => p in TAUT A by A1, Th3; :: thesis: verum