reserve A,B,C for Ordinal,
        o for object,
        x,y,z,t,r,l for Surreal,
        X,Y for set;

theorem Th23:
  - 0_No = 0_No
proof
  - 0_No = [--R_0_No, --L_0_No] by  Th7;
  hence thesis by Th22;
end;
