Definition:Language of Propositional Logic/Alphabet/Sign/Bracket

Definition
The signs of the language of propositional calculus include the brackets:

These are used as parenthesis signs.

Also defined as
Some sources use square brackets: $[$ and $]$ instead of the round brackets $($ and $)$. No doubt there are sources which use a different shape. The choice is arbitrary.

Some treatments of propositional logic do not specify brackets at all, having constructed the rules of formation to make them unnecessary.