Proof Explorer - Home Page - MetamathThe aleph null above is the symbol for the first infinite cardinal number, discovered by Georg Cantor in 1873 (see theorem aleph0). This is the starting page for the Metamath Proof Explorer subproject (set.mm database). See the main Metamath Home Page for an overview of Metamath and download links. If you wish to contribute your own proofs to the Metamath project, see How can I contribute to Metam
