I considered deleting the post, but this seems more cowardly than just admitting I was wrong. But TIL something!

  • @FishFace
    link
    69 months ago

    There is a function which, for each real number, gives you a unique number between 0 and 1. For example, 1/(1+e^x). This shows that there are no more numbers between 0 and 1 than there are real numbers. The formalisation of this fact is contained in the Cantor-Schröder-Bernstein theorem.

    • @lemmington_steele
      link
      19 months ago

      ah, but don’t forget to prove that the cardinality of [0,1] is that same as that of (0,1) on the way!

      • @FishFace
        link
        39 months ago

        This is pretty trivial if you know that the cardinality of (0, 1) is the same as that of R ;)

      • lad
        link
        fedilink
        19 months ago

        Isn’t cardinality of [0, 1] = cardinality of {0, 1} + cardinality of (0, 1)? One part of the sum is finite thus doesn’t contribute to the result

        • @lemmington_steele
          link
          2
          edit-2
          9 months ago

          technically yes, but the proof would usually show that this works by constructing the bijection of [0,1] and (0,1) and then you’d say the cardinalities are the same by the Schröder-Berstein theorem, because the proof of the latter is likely not something you want to demonstrate every day