It is a fixed rule with the wise never to defend themselves with the pen.

智者不会用笔来为自己辩解，这已是永恒的法则。

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But a life of beauty does have a fixed rule, which is to feel satisfied with your present.

但是，美丽人生的一条铁律，就是随遇而安。

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The system is a fixed rule, with the main characteristics of being mandatory, standard and objective.

制度是一种定型化了的规范，强制性、规范性和客观性是制度的主要特征。

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Today at Holyrood there was a startling departure from this fixed rule of political life.

BBC: Back on the beat

The rule of thumb is to use your age as a percentage of your savings to allocate to fixed income based funds (cash and bond funds) and the rest in stock funds (e.g. if you are 35, you might put 35% in bonds, 65% in stocks).

FORBES: How To Give Your 401(k) A Quick Check-Up To Put You In Better Position For A Strong Retirement

By coincidence, the central bank on Monday approved a new rule designed to protect consumers from deceptive lending practices, including advertising practices that say interest rates are fixed when in fact they're not.

FORBES: The Fed As Super-Regulator