Informally, a handle of a string is a substring that matches the right side of a production rule. But not every substring matches the right side of a production rule is handle A handle of a right sentential form g (= abw ) is a production rule A → b and a position of g where the string b may be found and replaced by A to produce the previous right-sentential form in a rightmost derivation of g . S ⇒(*|rm) a A w ⇒(*|rm) abw If the grammar is unambiguous, then every right-sentential form of the grammar has exactly one handle. We will see that w is a string of terminals.