37 C.F.R. 41.202 Suggesting an interference.

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1. (b) Patentee. A patentee cannot suggest an interference under this section but may, to the extent permitted under § 1.291 of this title, alert the examiner of an application claiming interfering subject matter to the possibility of an interference.

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A patentee may not suggest an interference unless it becomes an applicant by filing a reissue application. A patentee may, however, to the limited extent permitted under 37 CFR 1.291, alert an examiner to the existence of interfering claims in an application. See MPEP §§ 1134 and 1901.