<A HREF="https://en.wikipedia.org/wiki/Charles_Sanders_Peirce">Charles Sanders Peirce</A> is credited with the "beth" ℶ notation, in a December 1900 letter to Cantor.

[![enter image description here][1]][1]

<A HREF="https://books.google.nl/books?id=fMHiBQAAQBAJ&pg=PA101">source</A>


  [1]: https://i.sstatic.net/v6beJ.png