theorem :: GATE_1:36

for a, b, c, d, e, f, g, h being set holds
( not AND8 (a,b,c,d,e,f,g,h) is empty iff ( not a is empty & not b is empty & not c is empty & not d is empty & not e is empty & not f is empty & not g is empty & not h is empty ) ) by Def30;