reserve V for non empty set,
  A,B,A9,B9 for Element of V;
reserve f,f9 for Element of Funcs(V);
reserve m,m1,m2,m3,m9 for Element of Maps V;

theorem Th17:
  Maps(A,B) c= Maps V
proof
  let z be object;
  assume z in Maps(A,B);
  then ex f being Element of Funcs(V) st z = [[A,B],f] & [[A,B],f] in Maps(V);
  hence thesis;
end;
