Section efdom.
Variable X : Ens.
Hypothesis i : IN X (Domain Zero).
Let Y := EV Zero X.
Let step1 : IN (PAIR X Y) Zero.
Proof EV_th1 Zero X i.
Proof EmptySet_th1 (PAIR X Y) step1.
End efdom.
Proof efdom_Out.

Theorem empty_function_domain : EQ Zero (Domain Zero).