let X be Subset of CQC-WFF; :: thesis: for p, q being Element of CQC-WFF holds X |- p => (('not' p) => q)
let p, q be Element of CQC-WFF ; :: thesis: X |- p => (('not' p) => q)
p => (('not' p) => q) in Cn X by Th29;
hence X |- p => (('not' p) => q) by Def9; :: thesis: verum