let q, r, p, s be Element of CQC-WFF ; :: thesis: (((q => r) => (p => r)) => s) => ((p => q) => s) in TAUT
(p => q) => ((q => r) => (p => r)) in TAUT by Th1;
hence (((q => r) => (p => r)) => s) => ((p => q) => s) in TAUT by Th2; :: thesis: verum