Define a context-free grammar $G$, a sentence of $G$ and the language $\mathcal{L}(G)$ generated by $G$.

For the alphabet $\Sigma=\{a, b\}$, which of the following languages over $\Sigma$ are contextfree? (i) $\left\{a^{2 m} b^{2 m} \mid m \geqslant 0\right\}$,

(ii) $\left\{a^{m^{2}} b^{m^{2}} \mid m \geqslant 0\right\}$.

[You may assume standard results without proof if clearly stated.]