let p, q be Element of CQC-WFF ; :: thesis: for X being Subset of CQC-WFF st X |- ('not' p) => q holds
X |- ('not' q) => p
let X be Subset of CQC-WFF; :: thesis: ( X |- ('not' p) => q implies X |- ('not' q) => p )
assume A1: X |- ('not' p) => q ; :: thesis: X |- ('not' q) => p
X |- (('not' p) => q) => (('not' q) => p) by CQC_THE1:59;
hence X |- ('not' q) => p by A1, CQC_THE1:55; :: thesis: verum