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;

theorem
  A+^1 = succ A
proof
  thus A+^1 = succ(A+^0) by Lm1,Th28
    .= succ A by Th27;
end;
