tial element of an arm's-length transaction, see Kimbell v. United States, supra at 263; Huber v. Commissioner[ Dec. 56,510(M)), T.C. Memo. 2006-96; Estate of Stone v. Commissioner[ Dec. 55,341(M)), T.C. Memo. 2003-309, although we find nothing in the record to persuade us either that the formula clauses were no