League\Period\Period::merge PHP Method

    public function merge(Period $arg)
    {
        $reducer = function (Period $carry, Period $period) {
            if ($carry->getStartDate() > $period->getStartDate()) {
                $carry = $carry->startingOn($period->getStartDate());
            }
            if ($carry->getEndDate() < $period->getEndDate()) {
                $carry = $carry->endingOn($period->getEndDate());
            }
            return $carry;
        };
        return array_reduce(func_get_args(), $reducer, $this);
    }