let A be QC-alphabet ; :: thesis: for p, q, r being Element of CQC-WFF A holds ((p => q) => r) => ((r => p) => p) in TAUT A
let p, q, r be Element of CQC-WFF A; :: thesis: ((p => q) => r) => ((r => p) => p) in TAUT A
( ((p => q) => p) => p in TAUT A & (((p => q) => p) => p) => (((p => q) => r) => ((r => p) => p)) in TAUT A ) by Lm14, Lm15;
hence ((p => q) => r) => ((r => p) => p) in TAUT A by CQC_THE1:46; :: thesis: verum