reserve fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  X,Y for set,
  x,y for object;
reserve e,u for set;

theorem Th74:
  for a,b being Ordinal st a+^b is natural holds a in omega & b in omega
by Th24,ORDINAL1:12;
