Idempotence

A function $f$ is idempotent if $f(x)=f(f(x))$.

Examples

  • Any constant function is idempotent.
  • The function $f(x)=x$ is idempotent.
  • The signum function is idempotent.
  • The absolute value function is idempotent.
  • The greatest integer function is idempotent, as is the least integer function.
  • Unions and intersections are idempotent, as $A \cup A$ and $A \cap A$ are both equal to $A$.

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