在创建事实时，必须将每个维度的键分配给它。

When a fact is created, the key from each dimension must be assigned to it.

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例如，要把f2键分配给命令，请按f2键。

For example, to assign F2 to the command, press the F2 key.

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对于任意键或任意历史标识符，在创建事实时，就必须将一个键分配给事实。

With arbitrary keys, or arbitrary history identifiers, a key must be assigned to a fact at the time the fact is created.

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