 In order to fill the parsing table, we have to establish what grammar rule the parser should choose if it sees a nonterminal "A" on the top of its stack and a symbol "a" on its input stream.It is easy to see that such a rule should be of the form "A" → "w" and that the language corresponding to "w" should have at least one string starting with "a".For this purpose we define the "First-set" of "w", written here as Fi("w"), as the set of terminals that can be found at the start of some string in "w", plus ε if the empty string also belongs to "w".