let A be QC-alphabet ; :: thesis: for p, q, r, s being Element of CQC-WFF A holds p => (((('not' p) => r) => s) => ((q => r) => s)) in TAUT A
let p, q, r, s be Element of CQC-WFF A; :: thesis: p => (((('not' p) => r) => s) => ((q => r) => s)) in TAUT A
( (('not' p) => q) => (((('not' p) => r) => s) => ((q => r) => s)) in TAUT A & ((('not' p) => q) => (((('not' p) => r) => s) => ((q => r) => s))) => (p => (((('not' p) => r) => s) => ((q => r) => s))) in TAUT A ) by Lm3, Lm5;
hence p => (((('not' p) => r) => s) => ((q => r) => s)) in TAUT A by CQC_THE1:46; :: thesis: verum