let p, q be Element of CQC-WFF ; :: thesis: for X being Subset of CQC-WFF st X |- p => ('not' q) holds
X |- q => ('not' p)
let X be Subset of CQC-WFF ; :: thesis: ( X |- p => ('not' q) implies X |- q => ('not' p) )
assume A1: X |- p => ('not' q) ; :: thesis: X |- q => ('not' p)
X |- (p => ('not' q)) => (q => ('not' p)) by CQC_THE1:98;
hence X |- q => ('not' p) by A1, CQC_THE1:92; :: thesis: verum