let Al be QC-alphabet ; :: thesis: for X being Subset of (CQC-WFF Al)
for p being Element of CQC-WFF Al holds X |- (('not' p) => p) => p
let X be Subset of (CQC-WFF Al); :: thesis: for p being Element of CQC-WFF Al holds X |- (('not' p) => p) => p
let p be Element of CQC-WFF Al; :: thesis: X |- (('not' p) => p) => p
(('not' p) => p) => p in Cn X by Th7;
hence X |- (('not' p) => p) => p by Def8; :: thesis: verum