Chartrand, Marcella, Millar, Catherine & Wiltshire, Edward (1997), English for Contract and Company law, London, Sweet and Maxwell.
Chishire, Geoffrey, Fifoot, Cecil & Furmstom (1991), The Law of Contract, Butterworths, London.
Con, way & Paul. R (1939), Outling of the Law of Contracts, Harmon Publications, scond edition, Newyork.
De La Morandier (1962), Droit Civil: les Obligations, 4éme, sirey, Paris.
Douglas, Whitman (1997), Legal Studies in Business, New York, West Publishing Company.
Fisk, McKee (1955), Applied Business Law, South-Western Publishing Company, seventh edition.
Guest, A. G. (1997), Chitty on Contract, twenty-third edition, Sweet and Maxell,.
Hamblin, C. (1982), Introduction to Commercial Law, second edition, Sweet and Maxwell, London.
Marty, Gabriel et Reyaud, Fierre (1989), Droit Civil: les Obligations, 2ém , sirey, Paris.
Mazeaud, Jean (1965), les Obligations, 5éme, Montchrestien, Paris.
Padfield, C. F. (2002), Law Made Simple, London, eleventh edition.
Salmondl, John & Williams, James (1945), Principles of the Contract, Seweet and Maxwell , second edition, London.
Slapper, Gary & Kelly, David (2010), English law, London and New York, Routledge-Cavendish, third edttion.
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