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 Th8:
  m = [[dom m,cod m],m`2]
proof
 consider f,A,B such that
A1: m = [[A,B],f] &( B = {} implies A = {})& f is Function of A,B
  by Th4;
  thus thesis by A1;
end;
