Diagonal argument
# Diagonal argument

A diagonal argument, in mathematics, is a technique employed in the proofs of the following theorems:

* Cantor's diagonal argument (the earliest)
* Cantor's theorem
* Russell's paradox
* Diagonal lemma
   * Gödel's first incompleteness theorem
   * Tarski's undefinability theorem
* Halting problem
* Kleene's recursion theorem
