The set $NR$ of all DNA strands with no repeated $C$ bases: DNA strings $($including the empty

string$)$ that DO NOT contain the substring $"$CC$."($Recall we define the set of all DNA strands

as $\{A,T,G,C{\}}^{**},$ which is the set of all strings made up some combination of the characters $"$A$",$

$"$T$","$G$",$ and $"$C$",$ as well as the empty string.$)$