let A be QC-alphabet ; :: thesis: for p, q, t being Element of CQC-WFF A holds (('not' p) => q) => (t => ((q => p) => p)) in TAUT A
let p, q, t be Element of CQC-WFF A; :: thesis: (('not' p) => q) => (t => ((q => p) => p)) in TAUT A
( t => ((('not' p) => p) => p) in TAUT A & (t => ((('not' p) => p) => p)) => ((('not' p) => q) => (t => ((q => p) => p))) in TAUT A ) by Lm4, Lm8;
hence (('not' p) => q) => (t => ((q => p) => p)) in TAUT A by CQC_THE1:46; :: thesis: verum