theorem Th50:
  x+{} = x
proof
A1: (numerator x)*^1 = numerator x & {}*^(denominator x) = {} by ORDINAL2:35,39
;
A2: (denominator x)*^1 = denominator x & (numerator x)+^{} = numerator x by
ORDINAL2:27,39;
  denominator {} = 1 & numerator {} = {} by Def8,Def9,Lm1;
  hence thesis by A1,A2,Th39;
end;
