Where one of the parties recognizes an ambiguity, a duty to inquire about the ambiguity is imposed on the discovering party.

凡一方当事人供认一个含糊的，有义务的含糊查询是在发现方规则。

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During her 11-year premiership, Margaret Thatcher was said to regularly inquire whether a member of her own party was "one of us" - that is, ideologically committed to the same policy goals as she and her allies.

BBC: Why do people keep lists of enemies?