let A be QC-alphabet ; :: thesis: for p, q, r being Element of CQC-WFF A holds ((('not' p) => q) => r) => (p => r) in TAUT A
let p, q, r be Element of CQC-WFF A; :: thesis: ((('not' p) => q) => r) => (p => r) in TAUT A
p => (('not' p) => q) in TAUT A by CQC_THE1:43;
hence ((('not' p) => q) => r) => (p => r) in TAUT A by Th2; :: thesis: verum