In T 473/13 the board considered the arguments and the supporting evidence (an affidavit by the project manager and inventor of the patent in suit) submitted by the respondent (patent proprietor) to be sufficient to discharge its initial burden of proving that there had been a confidentiality agreement. The burden of proof then shifted to the intervener, which had to establish that there had been no such confidentiality agreement. The intervener had, however, presented no arguments or evidence which objectively might cast doubt on the existence of a confidentiality agreement, but had merely presented speculation in this respect. The intervener did not try to contact the utility company V, with which the patent proprietor had a co-operation, to enquire of them whether they considered a confidentiality agreement to have been in place. The intervener also did not make enquiries of other organisations active in the technical field in order to address the question whether such confidentiality agreements represented normal practice. The board concluded that the public nature of the prior use was not proven, such that it did not form part of the prior art.