let A be QC-alphabet ; :: thesis: for p, q being Element of CQC-WFF A holds ((p => q) => p) => p in TAUT A
let p, q be Element of CQC-WFF A; :: thesis: ((p => q) => p) => p in TAUT A
( (('not' p) => (p => q)) => (((p => q) => p) => p) in TAUT A & ((('not' p) => (p => q)) => (((p => q) => p) => p)) => ((p => (('not' p) => q)) => (((p => q) => p) => p)) in TAUT A ) by Lm11, Lm13;
then ( p => (('not' p) => q) in TAUT A & (p => (('not' p) => q)) => (((p => q) => p) => p) in TAUT A ) by CQC_THE1:43, CQC_THE1:46;
hence ((p => q) => p) => p in TAUT A by CQC_THE1:46; :: thesis: verum