Cantor's theorem states that the cardinal number of any set is lower than the cardinal number of
the set of all its subsets. A corollary is that there
is no highest 
(aleph).
Cantor's Theorem
See also
Cantor's ParadoxExplore with Wolfram|Alpha
References
Mendelson, E. Introduction to Mathematical Logic, 4th ed. London, England: Chapman & Hall, pp. 257 and 295, 1997.Suppes, P. Axiomatic Set Theory. New York: Dover, p. 97, 1972.Referenced on Wolfram|Alpha
Cantor's TheoremCite this as:
Weisstein, Eric W. "Cantor's Theorem." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CantorsTheorem.html