:: deftheorem Def21 defines NOR5 GATE_1:def 21 :
for a, b, c, d, e 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 NOR5 (a,b,c,d,e) = 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 ) implies NOR5 (a,b,c,d,e) = {} ) );