An SEC registrant must file a Form 8-K when its external auditor resigns, declines to stand for reelection, or is dismissed.
No one needs to file any forms when an auditor resigns 
mnli hypothesis: No one needs to file any forms when an auditor resigns  premise: An SEC registrant must file a Form 8-K when its external auditor resigns, declines to stand for reelection, or is dismissed.