reserve A,A1,A2,B,C,D for Ordinal,
  X,Y for set,
  x,y,a,b,c for object,
  L,L1,L2,L3 for Sequence,
  f for Function;
reserve fi,psi for Ordinal-Sequence;
reserve e,u for set;

theorem Th48:
  e in rng psi implies e is Ordinal
proof
  assume e in rng psi;
  then ex u being object st u in dom psi & e = psi.u by FUNCT_1:def 3;
  hence thesis;
end;
