let A be QC-alphabet ; :: thesis: for p, q being Element of CQC-WFF A holds (('not' p) '&' ('not' q)) => ('not' (p 'or' q)) in TAUT A
let p, q be Element of CQC-WFF A; :: thesis: (('not' p) '&' ('not' q)) => ('not' (p 'or' q)) in TAUT A
'not' (p 'or' q) = 'not' ('not' (('not' p) '&' ('not' q))) by QC_LANG2:def 3;
hence (('not' p) '&' ('not' q)) => ('not' (p 'or' q)) in TAUT A by LUKASI_1:27; :: thesis: verum