(a) Any paper submitted by the applicant in the course of the international procedure provided for in the Treaty and these Regulations, other than the international application itself, shall, if not itself in the form of a letter, be accompanied by a letter identifying the international application to which it relates. The letter shall be signed by the applicant.

(b) If the requirements provided for in paragraph (a) are not complied with, the applicant shall be informed as to the non-compliance and invited to remedy the omission within a time limit fixed in the invitation. The time limit so fixed shall be reasonable in the circumstances; even where the time limit so fixed expires later than the time limit applying to the furnishing of the paper (or even if the latter time limit has already expired), it shall not be less than 10 days and not more than one month from the mailing of the invitation. If the omission is remedied within the time limit fixed in the invitation, the omission shall be disregarded; otherwise, the applicant shall be informed that the paper has been disregarded.

(c) Where non-compliance with the requirements provided for in paragraph (a) has been overlooked and the paper taken into account in the international procedure, the non-compliance shall be disregarded.

(a) Subject to Rules 55.1 and 55.3 and to paragraph (b) of this Rule, any letter or document submitted by the applicant to the International Searching Authority or the International Preliminary Examining Authority shall be in the same language as the international application to which it relates. However, where a translation of the international application has been transmitted under Rule 23.1(b) or furnished under Rule 55.2, the language of such translation shall be used.
(b) Any letter from the applicant to the International Searching Authority or the International Preliminary Examining Authority may be in a language other than that of the international application, provided the said Authority authorizes the use of such language.
(c) [Deleted]
(d) Any letter from the applicant to the International Bureau shall be in English or French.
(e) Any letter or notification from the International Bureau to the applicant or to any national Office shall be in English or French.

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Where any international application indicates two or more applicants, it shall be sufficient, for the purpose of identifying that application, to indicate, in any Form or correspondence relating to such application, the name of the applicant first named in the request. The provisions of the first sentence of this Section do not apply to the demand.

(a) Any interested party may offer evidence that he has mailed the document or letter five days prior to the expiration of the time limit. Except in cases where surface mail normally arrives at its destination within two days of mailing, or where no airmail service is available, such evidence may be offered only if the mailing was by airmail. In any case, evidence may be offered only if the mailing was by mail registered by the postal authorities.
(b) If the mailing, in accordance with paragraph (a), of a document or letter is proven to the satisfaction of the national Office or intergovernmental organization which is the addressee, delay in arrival shall be excused, or, if the document or letter is lost in the mail, substitution for it of a new copy shall be permitted, provided that the interested party proves to the satisfaction of the said Office or organization that the document or letter offered in substitution is identical with the document or letter lost.
(c) In the cases provided for in paragraph (b), evidence of mailing within the prescribed time limit, and, where the document or letter was lost, the substitute document or letter as well as the evidence concerning its identity with the document or letter lost shall be submitted within one month after the date on which the interested party noticed or with due diligence should have noticed the delay or the loss, and in no case later than six months after the expiration of the time limit applicable in the given case.
(d) Any national Office or intergovernmental organization which has notified the International Bureau that it will do so shall, where a delivery service other than the postal authorities is used to mail a document or letter, apply the provisions of paragraphs (a) to (c) as if the delivery service was a postal authority. In such a case, the last sentence of paragraph (a) shall not apply but evidence may be offered only if details of the mailing were recorded by the delivery service at the time of mailing. The notification may contain an indication that it applies only to mailings using specified delivery services or delivery services which satisfy specified criteria. The International Bureau shall publish the information so notified in the Gazette.
(e) Any national Office or intergovernmental organization may proceed under paragraph (d):

(i) even if, where applicable, the delivery service used was not one of those specified, or did not satisfy the criteria specified, in the relevant notification under paragraph (d), or
(ii) even if that Office or organization has not sent to the International Bureau a notification under paragraph (d).