theorem Th41:
  m = [[dom m,cod m],m`2]
proof
  consider f,T1,T2 such that
A1: m = [[T1,T2],f] and
  T2`2 = {} implies T1`2 = {} and
  f is Function of T1`2,T2`2 and
  for x,y st [x,y] in T1`1 holds [f.x,f.y] in T2`1 by Th39;
  thus thesis by A1;
end;
