theorem
  Funcs(X --> Y, Z) = X --> Funcs(Y,Z)
proof
A1: X = dom (X --> Y);
A2: now
    let x be object;
    assume
A3: x in X;
    then Funcs(X --> Y, Z).x = Funcs((X --> Y).x,Z) by A1,Def7;
    hence Funcs(X --> Y, Z).x = Funcs(Y,Z) by A3,FUNCOP_1:7;
  end;
  dom Funcs(X --> Y, Z) = dom (X --> Y) by Def7;
  hence thesis by A2,FUNCOP_1:11;
end;
