此外，本系统中的各组原始公理还是自足的，即如想推出只含某些函数符号的永真公式时只须使用相应的公理便成。

This system is self-suffient in the sense that if we wish to deduce an equality involving only some of the three functions, then we need only to make use of the corresponding axioms.

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如果第一个条件不为真（意味着那个单元格有个80+的数字），那么Excel就会评估“三个符号”规则，并且在单元格中放置一个红色的“X”。

If the first rule is not true (meaning the cell has a number 80+), Excel evaluates the "three symbols" rule, and puts a red "X" in the cell.

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