let Al be QC-alphabet ; :: thesis: for X being Subset of (CQC-WFF Al)
for p, q being Element of CQC-WFF Al holds X |- p => (('not' p) => q)
let X be Subset of (CQC-WFF Al); :: thesis: for p, q being Element of CQC-WFF Al holds X |- p => (('not' p) => q)
let p, q be Element of CQC-WFF Al; :: thesis: X |- p => (('not' p) => q)
p => (('not' p) => q) in Cn X by Th8;
hence X |- p => (('not' p) => q) by Def8; :: thesis: verum