37 CFR 41.203: Declaration.

(a) Interfering subject matter. An interference exists if the subject matter of a claim of one party would, if prior art, have anticipated or rendered obvious the subject matter of a claim of the opposing party and vice versa.

(b) Notice of declaration. An administrative patent judge declares the patent interference on behalf of the Director. A notice declaring an interference identifies:

(1) The interfering subject matter;

(2) The involved applications, patents, and claims;

(3) The accorded benefit for each count; and

(4) The claims corresponding to each count.

(c) Redeclaration. An administrative patent judge may redeclare a patent interference on behalf of the Director to change the declaration made under paragraph (b) of this section.

(d) A party may suggest the addition of a patent or application to the interference or the declaration of an additional interference. The suggestion should make the showings required under § 41.202(a) of this part.