as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
system
give an example of a context-free grammar.
user
a simple example of a context-free grammar is the following: 

s → a b
a → c
b → d | e
c → f
d → g
e → g
f → a
g → b

this grammar has one start symbol (s), three non-terminal symbols (a, b and c) and two terminal symbols (a and b). it has two production rules: s → a b, and c → f. this grammar generates strings of symbols of the form a b b.
assistant