Cantor's theorem

Etymology
Named after German mathematician (1845-1918) who stated and proved this theorem.

Proper noun

 * 1)  A theorem in set theory which states for any set $$A$$, the set of all subsets of $$A$$ (the power set of $$A$$, denoted by $$\mathcal{P}(A)$$) has a strictly greater cardinality than $$A$$ itself.