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bfv  ·  43 days ago  ·  link  ·    ·  parent  ·  post: Teaching stuff is resolved.

    WHAT is indeed an invariant of the operation? What are we defining here? An integer plus its negative integer will equal zero - so is that an invariant operation? But that's "invariant" as adjective, not "an invariant" as noun.

The invariant is a property. If you're a mathematician, a property is a thing you can define an indicator function for.