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ironclad rule; inviolable rule; invariable principle; iron law
失敗したらすぐ報告するのが鉄則だ。
Reporting failures immediately is an ironclad rule.
料理での鉄則は、食材の鮮度を優先することだ。
The cardinal rule of cooking is to prioritize the freshness of ingredients.
相手の話をよく聞くのは交渉の鉄則だ。
Listening carefully to the other party is a cardinal rule of negotiation.