4.3.2 Public prior use
Overview
Although the standard of proof is the same for all objections covered by Art. 100 EPC (cf. T 270/90, OJ 1993, 725), the case law identifies two levels or standards of proof to be applied with regard to disputes around public prior use – either the "balance of probabilities" or "up to the hilt".
About burden of proof, see decision T 2037/18, which sets out detailed reasons on the issue (prior use; distinction between the admissibility and the substantive merits of the opposition; burden of presentation and burden of proof; principle of "negativa non sunt probanda"; non-confidentiality clause; shifting of the burden of proof) and cites numerous other decisions.