> The prof's definition begs the question. It was good enough for Russell so I doubt that. See https://en.wikipedia.org/wiki/Set-theoretic_definition_of_natur

> The prof's definition begs the question. It was good enough for Russell so I doubt that. See https://en.wikipedia.org/wiki/Set-theoretic_definition_of_natural_numbers#Definition_by_Frege_and_Russell https://en.wikipedia.org/wiki/Set-theoretic_definition_of_na...