Refers to a decision Blonder-Tongue Labs., Inc. v. University of Ill. Foundation, 402 U.S. 313 (1971) in which the US Supreme Court held that a decision that a patent was invalid in any Federal District Court precluded re-litigating the question of validity against a different defendant in a different Federal District. Before Blonder Tongue it was, curiously possible, to argue that a decision on validity in a particular Federal District was merely law of the District and didn’t preclude continuing enforcement of the patent in other Federal District courts against other defendants. Outside the Unified Patent Court or UPC, the same principle does not apply to European Patents; however, national court decisions on validity can be highly influential on other national courts.