A classification for prior art references established by WIPO in Standard ST. 14 for patent search reports. The Y classification means that the reference, when combined with another Y-reference, anticipates the invention. Y references may preclude a patent in Europe and Japan, particularly if they are in the same field. The U.S. usually requires some impetus in the references themselves that would suggest combination. Search report with an Y-References are not automatically considered to be non-clean search report. However, the existence of an Y-References does not mean that no patent can be secured – it may, for example, not apply to all the dependent claims and it is also possible that the searcher may have fundamentally misunderstood the gist of the invention. See A-Reference, X-Reference, E-Reference, and P-Reference.