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You will find many Google hits for this, including hits that deal with corporate finance.

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See Peter Cox's answer in the link below. This are in the memorandum accounts and not on the balance sheet because unlike provisions for charges and liabilities which are certain but of unknown timing or amount. These are only possible. They are also generally about one tenth the size of the others. See the second link to the Internationa Accounting Standard. "improprio" just means that the liabilities are to third parties, outside the company or group.