Prohibited benefit use by trust members limits tax exemption where trust income, property, or investments advantage insiders. Section 13(2) deems trust income or property to be used for the benefit of specified persons when transactions with them occur: loans without adequate interest or security; use of trust property without adequate rent; excess or inadequate payments for services; purchases or sales at excessive or inadequate consideration; diversion of income or property beyond a small threshold; and investments in concerns where those persons have a substantial interest. Section 13(4) preserves exemption for other income when aggregate investment in such a concern does not exceed a de minimis portion of its capital. 'Substantial interest' is defined by reference to voting power in companies and profit entitlement in other concerns.