For each regular language, give a regular expression to generate this language.

Question

For each regular language, give a regular expression to generate this language. For each context free language, give a context-free grammar. For the languages that are not context-free, no proof is necessary.
A - All strings over the alphabet {a, b, c, d} with at least four instances of c and at least two instances of a

B - All strings over the alphabet {a, b, c, d} where there are more a's than d's

C - All strings over the alphabet {a, b, c, d} where no b is immediately followed by an a and no c is immediately followed by a d.

D - All binary (alphabet {0,1}) strings which represent integers in the Fibonacci series (integers encoded in the normal way, no leading zeros)

E - All binary strings which represent multiples of 3 (all strings are nonnegative integers encoded in the normal way).

F - All strings over the alphabet {a, b, c, d} where there are at least three times as many a’s as b’s

Explanation / Answer

f (a^3n + b^n + c* + d* )*

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