1. The part of the judgment of the court of first instance against Defendant B and C is modified and reduced by this court.

1. Scope of the judgment of this court;

A. Subjective preliminary co-litigation of the relevant legal doctrine is a form of litigation in which all co-litigants settle the dispute between each other with respect to the same legal relationship in a lump sum without contradiction, and must be decided on the claims against all co-litigants.

(Article 70(2) of the Civil Procedure Act and where one of the main co-litigants and the conjunctive co-litigants files an appeal in a subjective preliminary co-litigation, the part of the claim related to other co-litigants shall be prevented, and they shall be subject to adjudication as they are transferred to the appellate court. In such a case, the appellate court shall determine the scope of adjudication in consideration of the need for the unity of conclusion between the main co-litigants and their other parties.

(see, e.g., Supreme Court Decision 2014Da75202, Mar. 20, 2015). Such a legal doctrine likewise applies to selective co-litigation (see, e.g., Supreme Court Decision 2010Da68237, Nov. 15, 2012).

Of the judgment of the first instance, the Plaintiff filed a claim against the Defendant B for the primary payment of the construction cost at the first instance court, and filed a claim against the Defendant C and D for the joint payment of the construction cost at the first instance court, and on the second instance, the Defendant B subrogated the claim against the said Defendant B for the joint payment of the construction cost, and as a preliminary claim, the claim against the Defendant B, C and D equivalent to the cost of materials and installation. (2) However, the claim against the Defendant C for the return of unjust enrichment at the second instance would be prepared against the case where the primary claim against the Defendant B is not accepted due to the absence of a claim for the construction cost.

The form of lawsuit is the defendant's preliminary co-litigation under Article 70 (1) of the Civil Procedure Act where a claim against a part of the co-litigants is legally incompatible with a claim against another co-litigants.

3. The judgment of the court of first instance is the same.