let A be QC-alphabet ; :: thesis: for p, q, r being Element of CQC-WFF A holds ((q => r) => p) => ((q => p) => p) in TAUT A
let p, q, r be Element of CQC-WFF A; :: thesis: ((q => r) => p) => ((q => p) => p) in TAUT A
( ((p => q) => q) => ((q => p) => p) in TAUT A & (((p => q) => q) => ((q => p) => p)) => (((q => r) => p) => ((q => p) => p)) in TAUT A ) by Lm16, Lm17;
hence ((q => r) => p) => ((q => p) => p) in TAUT A by CQC_THE1:46; :: thesis: verum