let A be QC-alphabet ; :: thesis: for p, q being Element of CQC-WFF A st p => ('not' q) in TAUT A holds
q => ('not' p) in TAUT A
let p, q be Element of CQC-WFF A; :: thesis: ( p => ('not' q) in TAUT A implies q => ('not' p) in TAUT A )
assume A1: p => ('not' q) in TAUT A ; :: thesis: q => ('not' p) in TAUT A
(p => ('not' q)) => (q => ('not' p)) in TAUT A by Th30;
hence q => ('not' p) in TAUT A by A1, CQC_THE1:46; :: thesis: verum