| Non-terminal | Terminals | Production Rule |
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The First and Follow sets are essential in the construction of parsers for context-free grammars (CFG). They help in determining the possible starting symbols of non-terminals and the possible lookahead symbols for a given grammar. These sets are particularly useful for LL(1) parsers. Here's a brief overview of what they represent:
The First set of a non-terminal is the set of terminals that begin the strings derivable from that non-terminal. If a non-terminal can derive an epsilon (empty string), then the First set will also include epsilon.
The Follow set of a non-terminal is the set of terminals that can appear immediately to the right of that non-terminal in some sentential form derived from the start symbol.
These sets are critical for deciding the next production rule to apply in a parser based on the lookahead symbol.