$(3$ points$)$ For an alphabet ${\displaystyle \underset{?}{\overset{?}{}}}=\{0,1\},$ a string xin${\displaystyle \underset{?}{\overset{?}{}}}**$ is called a palindrome if $x=x^R,$ that

is$,x$ is equal to its reversal. Let Asube${\displaystyle \underset{?}{\overset{?}{}}}**,$ where $A=\{xin{\displaystyle \underset{?}{\overset{?}{}}}**|x=x^R\}.$ Define the language $A$

recursively?