Chapter 4, Problem 19RQ

Explanation of Solution

Phrase of a sentential form:

Phrase in a parse tree is the string of terminals collected from the leaves of the partial parse tree, rooted at one specific internal node in the original parse tree. Now we can define phrase in a sentential form more precisely.

• Phrase can be used to define handle in the right sentential. For a right sentential form $\gamma =\alpha \beta w$, $\beta$ is the handle if and only if $\text{S }\Rightarrow {\text{*}}_{\text{rm}}\text{αAw }\Rightarrow {}_{\text{rm}}\text{αβw}$.
• This means that $\beta$ is the handle $\gamma =\alpha \beta w$ , if $\beta$ can be reduced to a non-terminal in one right most derivation (A) and resulting sentential form can be reduced to the start symbol on zero or more right most derivations