In formal language theory, a leftist grammar is a formal grammar on which certain restrictions are made on the left and right sides of the grammar's productions. Only two types of productions are allowed, namely those of the form [math]\displaystyle{ a \to ba }[/math] (insertion rules) and [math]\displaystyle{ cd \to d }[/math] (deletion rules). Here, [math]\displaystyle{ a,b,c }[/math] and [math]\displaystyle{ d }[/math] are terminal symbols. This type of grammar was motivated by accessibility problems in the field computer security.[1]
The membership problem for leftist grammars is decidable.[1]
Original source: https://en.wikipedia.org/wiki/Leftist grammar.
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