(A) Definition. Intervention takes place when a third person is permitted to become a party to an action between other persons, either by joining the plaintiff in claiming what is sought by the complaint, by uniting with the defendant in resisting the claims of the plaintiff, or by demanding something adversely to both the plaintiff and defendant.(B) Intervention of right. At any time before trial, any person shall be permitted to intervene in an action when a statute of this state, these rules, or the common law, confers an unconditional right to intervene.(C) Permissive intervention. At any time before trial, any person who has an interest in the matter in litigation may, by leave of court, intervene. In exercising its discretion, the court shall consider whether the intervention will unduly delay or prejudice the adjudication of the rights of the original parties.(D) Procedure. A person desiring to intervene shall serve a motion to intervene upon the parties as provided in Rule 9. The motion shall state the grounds therefor and shall be accompanied by a pleading setting forth the claim or defense for which intervention is sought. If the court allows the intervention, parties shall, within 10 days, file those responsive pleadings which are permitted or required by these rules for such pleading.CCP 12/2/1978; §B amended by 1979 c.284 § 21