Let $L$ be a given context-free language over the alphabet $\{a, b\}$ then $L_{2} = L·L$ is $\text{CFL.}$
Is $\text{CFL.}$ in general closed under $\text{self-concatenation?}$
If $L={ a^nb^n }$ then $L.L= { a^nb^na^nb^n }$ $\text{(or)}$ $L.L= { a^nb^na^mb^m } ?$