class Symbols  {
  private StringBuffer me = new StringBuffer () ;
  boolean mem(char c) {
    int len = me.length() ;
    for (int i = 0 ; i < len ; i++)
      if (me.charAt(i) == c)
        return true ;
    return false ;
  }

  boolean add (char c) {
    if (!mem(c)) {
      me.append(c) ;
      return true ;
    } else {
      return false ;
    }
  }

  char next() {
    for (char c = 'A' ; c <= 'Z' ; c++) {
      if (!mem(c)) {
        me.append(c) ;
        return c ;
      }
    }
    System.err.println("Ensemble plein") ;
    System.exit(2) ;
    return '\0' ;
  }

  public String toString() {
    return me.toString() ;
  }

  List toList() {
    List r = null ;
    for (int i = me.length()-1 ; i >= 0 ; i--)
      r = new List(me.charAt(i), r) ;
    return r ;
  }
}