n6 A covenant against conveyances and encumbrances is sometimes referred to as a "negative pledge" agreement. (See G. Osborne, Mortgages (1951) §§ 43-44; Coogan, Kripke, and Weiss, The Outer Fringes of Article 9: Subordination Agreements, Security Interests in Money and Deposits, Negative Pledge Clauses, and Participation Agreements (1965) 79 Harv.L.Rev. 229, 263-264; Comment (1965) 12 U.C.L.A. L.Rev. 954-962; but see CEB, § 2.37.) As summarized in the article by Coogan, Kripke, and Weiss: "The case law in this area is rather thin and in general dates from the depression. It indicates that a purely negative covenant creates no security interest in the property described."  . . .