In T 1056/01
the board pointed out that because of the crucial effect a valid priority date had on patentability, the date of filing of the application whose priority was claimed had to be proven in a formal way, namely by a certificate issued by the authority which had received that application (see R. 38(3) EPC 1973
, now R. 53(1) EPC
; and Art. 4D(3) Paris Convention). Even if no such formal proof
was prescribed for the timely withdrawal of a previous application pursuant to Art. 87(4) EPC 1973
(see Art. 4C(4) Paris Convention), it appeared appropriate to require an equally high standard of proof, for once there existed a previous application concerning the same invention both dates were equally relevant for establishing the validity of the claimed priority. However, in the case at issue, the timely withdrawal of the UK application for the purposes of Art. 87(4) EPC 1973
could not be established. Unlike facts barring patentability (see for example T 219/83
cited by the appellant), the timely withdrawal of a previous application was a positive precondition for claiming a valid priority from a subsequent application for the same invention. Hence, the date of the effect of the withdrawal was a fact which could act in the applicant’s favour, and she had relied on it just as she had relied on the filing date (and the content) of the subsequent UK application.