References to scholarly articles or to patents. Thus the front page of a U.S. patent usually contains a list of citations, i.e., prior art considered in the course of the application (which typically are mostly other patents). A superscript star (*) is usually placed next to art specifically reviewed and discussed by the examiner. It is extremely difficult to overturn the validity of a patent by reliance on prior art found in the list of citations, because it is presumed (not necessarily accurately) that the patent office properly reviewed such art.