Formal language

A formal language $L$ with an alphabet $𝐴$ is a set of strings in the alphabet $𝐴$ , i.e. a subset of the free monoid $𝐴 *$ . logic The strings in $L$ are called well-formed formulae or just formulae of $L$ . Usually there is an effective procedure for determining if a given string is a formula of $L$ , e.g. as defined by a formal grammar.