Chapter 4, Problem 18RQ

Explanation of Solution

Definition of Left factoring:

Left factoring is used when the parser has to choose between the RHSs of a non-terminal while expanding a non-terminal, where there are multiple RHS for the same non terminal starting with the same terminal symbol.

Example:

A aB / a

This production cannot pass the pairwise disjoint test as

$\begin{array}{l}\text{First}\left(\text{aB}\right)\text{=}\text{a}\\ \text{First}\left(\text{a}\right)\text{=}\text{a}\\ \text{First}\left(\text{aB}\right)\cap \end{array}$