let A be QC-alphabet ; :: thesis: for p, q, r, t being Element of CQC-WFF A holds ((t => ((q => p) => p)) => r) => ((('not' p) => q) => r) in TAUT A
let p, q, r, t be Element of CQC-WFF A; :: thesis: ((t => ((q => p) => p)) => r) => ((('not' p) => q) => r) in TAUT A
( (('not' p) => q) => (t => ((q => p) => p)) in TAUT A & ((('not' p) => q) => (t => ((q => p) => p))) => (((t => ((q => p) => p)) => r) => ((('not' p) => q) => r)) in TAUT A ) by Lm9, Th1;
hence ((t => ((q => p) => p)) => r) => ((('not' p) => q) => r) in TAUT A by CQC_THE1:46; :: thesis: verum