The handwritten letter of guarantee is established and has legal effect after being confirmed by signature and seal, provided that it does not violate the mandatory provisions of the law and is true. A civil juristic act in which the actor and the counterpart have false meanings is invalid. The validity of a concealed civil juristic act with false intention shall be handled in accordance with relevant laws and regulations. Article 146 of the Civil Code stipulates that the civil legal acts carried out by the actor and the counterpart for false intentions are invalid. The validity of a concealed civil juristic act with false intention shall be handled in accordance with relevant laws and regulations. Article 153 A civil juristic act that violates the mandatory provisions of laws and administrative regulations is invalid. However, unless mandatory provisions do not invalidate civil legal acts. A civil legal act that violates public order and good customs is invalid. Article 154 A civil legal act in which the actor colludes with the counterpart in bad faith and damages the legitimate rights and interests of others is invalid. Article 490 Where the parties conclude a contract in the form of a contract, the contract is formed when the parties sign, seal or fingerprint it. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it.