If the same legal person signs a supplementary contract, the subsequent supplementary contract will be valid, and for the same problem, the subsequent contract will be more effective than the previous one.

A supplementary contract will only be legally effective if it meets the following conditions:

The parties to the contract have corresponding civil rights and civil capacity. If the subject fails, the contract will not be legally effective.

The expression of intention of the parties to a contract means that the actor's expression of intention should truly reflect his inner intention. After a contract is established, it is often difficult to judge from the outside whether the parties’ intentions are true or not, and the law generally does not actively intervene in this matter. Lack of the requirement of true expression of intention, even if the expression of intention is untrue, does not absolutely render the contract invalid.

The contract does not violate the law or social welfare interests. The contract does not violate the law or social welfare interests. It mainly includes two meanings:

The content of the contract is legal, that is, the contract The rights and obligations agreed in the terms are in compliance with the provisions of the law.

The purpose of the contract is legal, that is, the reasons for the parties to enter into the contract are legal, and there are no facts to circumvent the law such as achieving illegal purposes in legal ways. It must have the formal requirements required by laws and administrative regulations for a contract to be effective. The so-called formal requirements refer to the formal requirements of laws and administrative regulations for a contract. The formal requirements are usually not the requirements for a contract to be effective, and are specifically stipulated by law.