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

Its category-theoretical general formulation is given by Lawvere's fixed-point theorem.