Problem $3$: Let $L=\{a^n{b}^n,n>0\},$

a$)$ Prove that $L^2$ is CFL

b$)$ Prove that $L^k$ is CFL$,$ where k is an integer greater than or equal to $1$

c$)$ Prove that the language, over alphabet $\{a,b,c\},$ that is comprised of strings that are comprised of only a$\text{'}$s or only b$\text{'}$s or only c$\text{'}$s$,$ is CFL