let A be QC-alphabet ; :: thesis: for p, q being Element of CQC-WFF A st ('not' p) => q in TAUT A holds
('not' q) => p in TAUT A
let p, q be Element of CQC-WFF A; :: thesis: ( ('not' p) => q in TAUT A implies ('not' q) => p in TAUT A )
assume A1: ('not' p) => q in TAUT A ; :: thesis: ('not' q) => p in TAUT A
(('not' p) => q) => (('not' q) => p) in TAUT A by Th31;
hence ('not' q) => p in TAUT A by A1, CQC_THE1:46; :: thesis: verum