defined (you dont define them, just use them). Do not use the extended BNF notation. not BNF. Clarification: alphabet is {0,1}. 'string' is the same as program in this context, but here the programs are written using the binary alphabet so strings here are binary. 3. For the above, how many valid strings there are? 4. For the above, how many valid strings are there if we restrict the total length to a) exactly 7 bits, and b ) at most 7 bits