Treasury Regulations (26 C.F.R.)
26 CFR § 1.860F-1 — Qualified liquidations.
A plan of liquidation need not be in any special form. If a REMIC specifies the first day in the 90-day liquidation period in a statement attached to its final return, then the REMIC will be considered to have adopted a plan of liquidation on the specified date.
Source: official text