theorem :: BVFUNC_6:81

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