Analysis of information sources in references of the Wikipedia article "Formation rule" in English language version.
Specifying the syntax of any language L follows a common pattern. First a set of symbols is given, and we define an L-expression to be any finite sequence of these symbols. Then we specify one or more sets of L-expressions which we regard as meaningful. The meaningful expressions are generally described as those constructed by following certain rules or algorithms, and the set of them is characterized as the smallest set of expressions which is closed under these formation rules.
