public RE extractRE() throws InterruptedException {
  arden();
  if (!coeffs.isEmpty()) {
    throw new RuntimeException("production still has free variables");
  }
  return unionREs(terms);
}

public RE extractRE ( ) throws InterruptedException { arden ( ) ; if ( ! coeffs . isEmpty ( ) ) { throw new RuntimeException ( "production still has free variables" ) ; } return unionREs ( terms ) ; }
extract the regular expression associated with this recursive production . fails if there are references to other productions in coeffs .
