How to Prove a Function Is Uncountably Infinite?

We say that |X| = |Y | if there exists a bijection f : X → Y . We say a set X is countably infinite if |X| = |N|. If X is infinite, but it is not countably infinite, we say that X is uncountably infinite, or just uncountable. A set X is called countable if it is either finite or countably infinite.

How do you prove something is Uncountably infinite?

A set is countably infinite if its elements can be put in one-to-one correspondence with the set of natural numbers. In other words, one can count off all elements in the set in such a way that, even though the counting will take forever, you will get to any particular element in a finite amount of time.

How do you prove a function is uncountable?

A set X is uncountable if and only if any of the following conditions hold:
  1. There is no injective function (hence no bijection) from X to the set of natural numbers.
  2. X is nonempty and for every ω-sequence of elements of X, there exist at least one element of X not included in it.
Marcus Vance

Marcus Vance

Cybersecurity & Digital Privacy Researcher

Marcus Vance is a cybersecurity auditor and technology writer dedicated to educating the public about online safety, data privacy regulations, enterprise security, and emerging cyber threats.