public static RE mkStar(RE x){
  if (x.equals(epsilon) || x.equals(empty)) {
    return epsilon;
  }
  RE res=new RE(ReOp.STAR);
  res.unaryArg=x;
  return res;
}

public static RE mkStar ( RE x ) { if ( x . equals ( epsilon ) || x . equals ( empty ) ) { return epsilon ; } RE res = new RE ( ReOp . STAR ) ; res . unaryArg = x ; return res ; }
construct a regular expression matching the kleene closure of the language matched by the argument regular expression .
