theorem :: BVFUNC_6:144

for Y being non empty set
for a, b, c being Function of Y,BOOLEAN holds ((a 'or' ('not' b)) '&' (b 'or' ('not' c))) '&' (c 'or' ('not' a)) = ((b 'or' ('not' a)) '&' (c 'or' ('not' b))) '&' (a 'or' ('not' c))