Rule 13. Counterclaim

(a) Compulsory Counterclaims. The answer shall state as a counterclaim any claim which, at the time of serving the answer, the defendant has against any plaintiff, if it arises out of the transaction or occurrence that is the subject matter of the opposing party's claim and does not require for its adjudication the presence of third parties of whom the court cannot acquire jurisdiction. But the answer need not state the claim if at the time the action was commenced the claim was the subject of another pending action.

(b) Permissive Counterclaims. The answer may state as a counterclaim any claim against an opposing party not arising out of the transaction or occurrence that is the subject matter of the opposing party's claim.

(c) Counterclaim Exceeding Opposing Claim. A counterclaim may or may not diminish or defeat the recovery sought by the opposing party. It may claim relief exceeding in amount or different in kind from that sought in the pleading of the opposing party.

(d) Counterclaim Against the United States. [Not used.]

(e) Counterclaim Maturing or Acquired After Pleading. A claim which either matured or was acquired by the defendant after serving its pleading may, with the permission of the court, be presented as a counterclaim by supplemental pleading.

(f) Omitted Counterclaim. When the defendant fails to set up a counterclaim through oversight, inadvertence or excusable neglect, or when justice requires, it may by leave of court set up the counterclaim by amendment.

(g) Cross-Claim Against Co-Party. [Not used.]

(h) Joinder of Additional Parties. [Not used.]

(i) Separate Trials; Separate Judgments. If the court orders separate trials as provided in Rule 42(b), judgment on a counterclaim may be rendered in accordance with the terms of Rule 54(b) when the court has jurisdiction so to do, even if the claims of the opposing party have been dismissed or otherwise disposed of.