All financial relations between a creditor and a customer, whether recorded in one record or in more than one record, shall be included in and be deemed to be part of the customer's general account with the creditor, * * *.
and § 220.2(c) defines the term "customer" to include
* * * any person, or any group of persons acting jointly, * * * to or for whom a creditor is extending or maintaining any credit * * *
In the course of a normal month's operations, both Firm X and Firm Y are at one time or another extending credit to the joint account, since both make purchases for the account that are not "settled" until the month's end. Consequently, the account would be a "customer" within the above definition.
* * * the adjusted debit balance of the account shall include, in addition to the items specified in § 220.3(d) , any amount by which the creditor's contribution to the joint adventure exceeds the contribution which he would have made if he had contributed merely in proportion to his right to share in the profits of the joint adventure.
In addition, the final paragraph of § 220.2(c) states that the definition of "customer"
* * * includes any joint adventure in which a creditor participates and which would be considered a customer of the creditor if the creditor were not a participant.
12 C.F.R. §220.121