
theorem
  for L being add-associative right_zeroed right_complementable
  right-distributive right_unital non empty doubleLoopStr, I being RightIdeal
  of L, x,y being Element of L st x in I & y in I holds x-y in I
proof
  let L being add-associative right_zeroed right_complementable
  right-distributive right_unital non empty doubleLoopStr;
  let I being RightIdeal of L;
  let x, y being Element of L;
  assume that
A1: x in I and
A2: y in I;
  - y in I by A2,Th14;
  hence thesis by A1,Def1;
end;
