let Al be QC-alphabet ; :: thesis: for X being Subset of (CQC-WFF Al)
for p, q, r being Element of CQC-WFF Al holds X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r)))
let X be Subset of (CQC-WFF Al); :: thesis: for p, q, r being Element of CQC-WFF Al holds X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r)))
let p, q, r be Element of CQC-WFF Al; :: thesis: X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r)))
(p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) in Cn X by Th9;
hence X |- (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) by Def8; :: thesis: verum