the Court observed that patent owners in district court enjoy a presumption of
patent validity that does not apply in post-grant proceedings where the burden
to demonstrate obviousness is by a preponderance of the evidence, rather than
by clear and convincing evidence.
United States intervened over OSI's other grounds for appeal, questioning the
constitutionality of subjecting to inter partes review proceedings patents
arising from applications filed before passage of the Leahy-Smith America