reserve A,B,O for Ordinal,
        o for object,
        x,y,z for Surreal,
        n,m for Nat;
reserve d,d1,d2 for Dyadic;
reserve i,j for Integer,
        n,m,p for Nat;

theorem Th21:
  INT = DYADIC(0)
proof
A1: 2|^0 = 1 by NEWTON:4;
  thus INT c= DYADIC(0)
  proof
    let o;
    assume o in INT;
    then reconsider o as Integer;
    o = o/(2|^0) by A1;
    hence thesis by Def4;
  end;
  let o;
  assume o in DYADIC(0);
  then ex i st o = i / (2|^0) by Def4;
  hence thesis by A1,INT_1:def 2;
end;
