The decree no. 81-255 of 3 March 1981 on the repression of fraud in art transactions and collections known as the "Marcus decree" sets out the formulas to be used to describe works of art in auction catalogs and, consequently, on purchase invoices. In fact, the description of an item followed by the name of an artist or a reference to a historical period, century, or era guarantees to the buyer that the item was produced by the artist or during the reference period (e.g., Cartier, Art Deco period). References that express uncertainty about the attribution of the work, such as "school of...", "after...", "in the style of", give an opinion of the expert but do not provide any guarantee as to that attribution.