No modification of the Contract is valid unless agreed or evidenced in writing.

5除非书面约定或证明，任何对合同的修改都是无效的。

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No addition or modification to this contract shall be valid unless made in writing.

除非以书面形式做成，对本合同所进行的补充和修改均无效。

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No changing or modification of this Agreement shall be valid unless the same is made in writing.

本协议之修改必须作成书面始生效力。

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The airport said it was carrying out a full investigation and that Ms Wilson had been banned from the airport, unless she had a valid reason to travel.

BBC: NEWS | UK | Scotland | Lap dancer breaches air security

Justices Scalia, Thomas and Alito wrote separately to say that in their view no voter has a valid claim against a law like this unless the voter can prove discriminatory intent.

NPR: High Court Supports Indiana Voter ID Law

You are insisting that we get to a very fundamental question about equal protection, but we don't do that unless we assume the law is valid otherwise to begin with.

WSJ: Best of the Web Today: Maybe Scalia Was Wrong