# Idempotence of a Function

How many of the following functions are idempotent?

• $$\lfloor x \rfloor$$

• $$|x|$$

• $$x^2$$

• $$\lceil x \rceil$$

• $$\sqrt{x}$$

• $$f(f(x))=f(x)$$

Definition: Idempotence

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