If the insured lies under oath the policy is void whether the lie is in a proof of loss or at an examination under oath. The lie could be on the proof of loss statement, statements made to the carrier about the claim, statements made in the examination under oath, statements made on the application that the insured knows to be false. The difference between fraud and false swearing is that since false swearing involves a false statement made under oath, it is harder for the person to back off from the false statements when confronted.