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

theorem Th61:
  for X,Y be set st
    for x st x in X ex y st y in Y & x==y holds X <=_ Y
proof
  let X,Y be set such that
  A1:for x st x in X ex y st y in Y & x==y;
  let x;assume x in X;
  then ex y st y in Y & x==y by A1;
  hence thesis;
end;
