:: deftheorem Def25 defines NOR6 GATE_1:def 25 :
for a, b, c, d, e, f being set holds
( ( not a is empty or not b is empty or not c is empty or not d is empty or not e is empty or not f is empty or NOR6 (a,b,c,d,e,f) = NOT1 {} ) & ( ( not a is empty or not b is empty or not c is empty or not d is empty or not e is empty or not f is empty ) implies NOR6 (a,b,c,d,e,f) = {} ) );