Editing Canonical LR parser (section)

=== FIRST and FOLLOW sets ===
To determine lookahead terminals, so-called FIRST and FOLLOW sets are used.
FIRST(A) is the set of terminals which can appear as the first element of any chain of rules  matching nonterminal A. FOLLOW(I) of an Item I [A → α • B β, x] is the set of terminals that can appear immediately after [[nonterminal]] B, where α, β are  arbitrary symbol strings, and x is an arbitrary lookahead terminal. FOLLOW(k,B) of an item set k and a nonterminal B is the union of the follow sets of all items in k where '•' is followed by B. The FIRST sets can be determined directly from the closures of all nonterminals in the language, while the FOLLOW sets are determined from the items under usage of the FIRST sets.

In our example, as one can verify from the full list of item sets below, the first sets are:
: FIRST(S) = { n, '+', '(' }
: FIRST(E) = { n, '+', '(' }
: FIRST(T) = { n, '+' }