private boolean isListSorted(List tl) {
        // tl must be populated with DateTime objects.
        DateTime lhDT = (DateTime)tl.get(0);
        DateTime rhDT = null;
        Long lhVal = new Long( lhDT.getMillis() );
        Long rhVal = null;
        for (int i = 1; i < tl.size(); ++i) {
            rhDT = (DateTime)tl.get(i);
            rhVal = new Long( rhDT.getMillis() );
            if ( lhVal.compareTo( rhVal) > 0 ) return false;
            //
            lhVal = rhVal;  // swap for next iteration
            lhDT = rhDT;    // swap for next iteration
        }
        return true;
    }