"A significant uncertainty in this area has been whether each investment held by a plan is a separate 'trade or business' (such that a plan must calculate its UBIT for each individual investment) or whether a plan can consider all investments of the same 'type' as a single trade or business (such that a plan can calculate its UBIT across all of these investments in the aggregate, netting gains and losses on the whole). [IRS Notice 2018-67] provided a variety of approaches that plans may apply to simplify the impact of this change. The Proposed UBIT Regulations retain many of the concepts included in the Notice but with some significant modifications."