let A be QC-alphabet ; :: thesis: for p, q, r, s being Element of CQC-WFF A holds (q => s) => (((q => r) => p) => ((s => p) => p)) in TAUT A
let p, q, r, s be Element of CQC-WFF A; :: thesis: (q => s) => (((q => r) => p) => ((s => p) => p)) in TAUT A
( ((q => r) => p) => ((q => p) => p) in TAUT A & (((q => r) => p) => ((q => p) => p)) => ((q => s) => (((q => r) => p) => ((s => p) => p))) in TAUT A ) by Lm4, Lm18;
hence (q => s) => (((q => r) => p) => ((s => p) => p)) in TAUT A by CQC_THE1:46; :: thesis: verum