Article 54(4). The deleted Article 54(4) EPC remains applicable to the European patents granted before December 13, 2007 and the European patent applications pending on December 13, 2007. In other words, Art. 54(4) EPC 1973 is still transitionally applicable. This amendment along with the absence of a transitional provision for Rule 23a (providing that Rule 23a EPC 1973 would continue to apply for pending applications or granted patents at the date of entry into force of the EPC 2000) has raised concerns that, "if the provisions of the EPC 2000 are interpreted strictly", patent rights existing at the date of entry into force of the EPC 2000 may become invalid after the entry into force of the EPC 2000, on December 13, 2007. In September 2007, the European Patent Office published a notice indicating that "the provisions currently laid down in Article 54(3) and (4) in conjunction with Rule 23a EPC 1973 will continue to apply to European patent applications filed and patents granted before the entry into force of the EPC 2000".<ref>EPO, [http://www.european-patent-office.org/epo/pubs/oj007/10_07/10_5047.pdf Notice from the European Patent Office dated 20 September 2007 on implementation of the transitional provisions of the EPC 2000 applicable during the transition from the EPC 1973 to the EPC 2000], Official Journal EPO 10/2007, p. 504.</ref> Requirements for obtaining a date of filing The requirements to obtain a date of filing (for a European patent application), laid out in Article 80, have been amended. A reference is now made to the Implementing Regulations, which are now in line with "the worldwide standard laid out in Article 5 of the Patent Law Treaty 2000 (PLT)". In particular, Rule 40 EPC 2000 is relevant. There is no requirement anymore to file claims to obtain a date of filing. In addition the description may be filed in any language. Among the requirements, a reference to a previously filed application may also be used to obtain a date of filing. Furthermore, filing by reference to a previously filed application may incorporate the claims of the previously filed application.Andrea Veronese & Peter Watchorn, Procedural law under the EPC-2000 (3rd Ed. May 2013), Kastner AG, , Chapter II.6.4 From December 13, 2007 to December 19, 2008, "54 applications [have] been received with a later date of receipt of claims than the original application date. Sixty-one invitations to file claims have been prepared for other applications missing the date of receipt