Now that you know a bit about BNF's, try writing a grammar(productions) for the "language" of a phonenumber, which consists of:

• three digits enclosed in parentheses - the first digit cannotbe "0" (zero)
• followed by three digits - the first digit cannot be "0"(zero)
• followed by a "-" (dash)
• followed by four digits

So, (757)530-4601 is a valid phone number. All the followingnumbers are invalidaccording to thisgrammar:

• 757-530-4601 (area code is not in parentheses)
• (757)530.4601 (missing dash after the exchange)
• (919)-555-5555 (stray dash after area code)
• (019)555-5555 (area code cannot start with zero)
• and so on

Once you have a grammar, write down:

• the derivation of one correct phonenumber - give both the sequence of substitutions and the parse treerepresentation

• the attempted derivationof one incorrect phone number - list thesequence of substitutions OR draw the parse tree until thederivation "breaks." Write a note explaining why the derivation cango no further.