The notion of provability itself can also be encoded by Gödel numbers, in the following way: since a proof is a list of statements which obey certain rules, the Gödel number of a proof can be defined. Now, for every statement "p", one may ask whether a number "x" is the Gödel number of its proof. The relation between the Gödel number of "p" and "x", the potential Gödel number of its proof, is an arithmetical relation between two numbers. Therefore, there is a statement form Bew("y") that uses this arithmetical relation to state that a Gödel number of a proof of "y" exists: