let X be Subset of CQC-WFF ; :: thesis: for p, q, r being Element of CQC-WFF holds X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r)))
let p, q, r be Element of CQC-WFF ; :: thesis: X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r)))
A1: (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) in Cn X by Th30;
thus X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) by A1, Def9; :: thesis: verum