let A be QC-alphabet ; :: thesis: for t, p being Element of CQC-WFF A holds t => ((('not' p) => p) => p) in TAUT A
let t, p be Element of CQC-WFF A; :: thesis: t => ((('not' p) => p) => p) in TAUT A
( (('not' t) => ((('not' p) => p) => p)) => ((('not' p) => p) => p) in TAUT A & ((('not' t) => ((('not' p) => p) => p)) => ((('not' p) => p) => p)) => (t => ((('not' p) => p) => p)) in TAUT A ) by Lm5, Lm7;
hence t => ((('not' p) => p) => p) in TAUT A by CQC_THE1:46; :: thesis: verum