最后一项操作尤为有用，因为它允许我们在树上执行符号操作。

The last operation is particularly useful because it lets us perform symbolic manipulations on the tree.

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但是，能够操作符号在大多数情况下还不足够。

But being able to manipulate symbols is not enough in most cases.

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要在程序内命名这些数量并使代码更易于阅读，可以通过. equ操作将符号赋予这些值。

To name these quantities within the program and make the code more readable, we give these values symbols through the.equ operation.

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