theorem :: ZF_LANG1:122

for p, q being ZF-formula
for M being non empty set
for v being Function of VAR,M holds
( M,v |= ('not' (p '&' q)) => (('not' p) 'or' ('not' q)) & M |= ('not' (p '&' q)) => (('not' p) 'or' ('not' q)) )