protected void slice_check()
    {
	if (bra < 0 ||
	    bra > ket ||
	    ket > limit ||
	    limit > current.length())   // this line could be removed
	{
	    System.err.println("faulty slice operation");
	// FIXME: report error somehow.
	/*
	    fprintf(stderr, "faulty slice operation:\n");
	    debug(z, -1, 0);
	    exit(1);
	    */
	}
    }