1. Of the part on the principal lawsuit in the judgment of the court of first instance, the part on the Defendant-Counterclaim Plaintiff is jointly and severally against the Plaintiff (Counterclaim Defendant).

1. Basic facts and the grounds for the court’s judgment on this part of the allegations by the parties are the same as the corresponding part of the judgment of the court of first instance, and thus, they shall be quoted in accordance with the main sentence of Article 420

2. We examine the principal lawsuit and the counterclaim together.

A. According to the purport of Gap evidence No. 2-1 and all pleadings as to the increase or decrease of construction cost, Article 6 of the instant contract

C. (1) Paragraph (1) provides that “The price adjustment and payment following the change of design, economic situation change, etc. shall be adjusted according to the contents and proportion thereof within 30 days from the date on which the ordering person was adjusted by the ordering person.

However, after the contract of this case, the volume of “AL E-TYE” (A-TYE) to be constructed on the part of the connecting passage (hereinafter “the connecting passage of this case”) according to the design change has decreased from 2,896 square meters to 2,655 square meters, and the Plaintiff and the Defendants agreed impliedly to the adjustment of the construction price pursuant to the design change during the construction of this case. As such, there is no dispute between the parties concerned, the construction cost of the construction of this case differs depending on whether the materials or construction method substituted for the connecting passage of this case “Alumn U.S.S.S./,” and “Aluminium panel” were “Aluminium panel”.

Therefore, the first instance court's appraiser F expressed to the first instance court the opinion that the material or construction method used as a substitute for the connecting passage part of this case "TRUSS/ frame, Corning" is "TRUSS", but on the other hand, according to the results of the fact-finding and the overall purport of oral argument on the Airport Support Department and the Seoul Regional Aviation Agency of this Court, it can be recognized that the connecting passage part of this case was installed in the main part, such as columns and beams, and that it is confirmed that the connecting passage part of this case was constructed in a public law with an Aluminium panel attached with an Aluminium panel. Thus, the fact-finding results and arguments with the first instance court F.