We can rely on informal documentation to specify such invariants, but the more invariants we can formalize and check, the better.

我们可以依靠非正式文件来规定这类不变量，我们标准化和检查的不变量越多，效果就越好。

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The higher fees and burdensome documentation requirements--such as proof of address and Social Security cards--pushed immigrants into informal channels to send money overseas more quickly, less expensively and with fewer questions.

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