T is a finite nonempty set of terminal symbols, which consist of strings in the language (such as while), which refer to parts of the text of sentences in the language.

if a context-free grammar is a tuple G = (T, N, S,P) what is N

N is a finite nonempty set of non-terminal symbols, disjoint from T. These refer to syntactic structures defined by other structures and rules (e.g., <exp>).

if a context-free grammar is a tuple G = (T, N, S,P) what is S

[1] The start symbol is that given on the left-hand-side of the first rule. [2] For each non-terminal symbol we use | to separate the alternative right-hand sides of the production rules.

write G2 in short hand G2 = (T, N, S, P) where T = {a, b}, N = {S, C} and P ={S →ε, S →C, S →aSa, S →bSb, C → a, C → b}.