let s, p, q, r be Element of CQC-WFF ; :: thesis: (s => (p => (q => r))) => ((q => s) => (p => (q => r))) in TAUT
( (q => s) => ((s => (p => (q => r))) => (p => (q => r))) in TAUT & ((q => s) => ((s => (p => (q => r))) => (p => (q => r)))) => ((s => (p => (q => r))) => ((q => s) => (p => (q => r)))) in TAUT ) by Lm21, Th8;
hence (s => (p => (q => r))) => ((q => s) => (p => (q => r))) in TAUT by CQC_THE1:82; :: thesis: verum