No principle requires that a witness testify as to legal conclusion of undue experimentation, provided factual showing is sufficient to justify jury’s conclusion on factual issue of whether, under all circumstances, more than routine experimentation is needed to make the invention work as claimed. Multiple prior art references offered to prove anticipation do not constitute multiple separate legal theories, each of which must to be proven to show anticipation. If any single reference shows anticipation, the legal theory of anticipation is met. Findings as to invalidity of claims apply only to asserted claims at an infringement trial.