The Question :

Prove that the following languages are context-free by giving grammars that accept them.

S = {$\displaystyle 0^i 1^j 2^k 3^l$ | i=k and j=l }

I felt like I could just substitute i = k and j = l, int the expression thus having to show that $\displaystyle 0^k 1^l 2^k 3^l $ has some CFG.

Is that enough? This is the result I got from doing that :

Let T=

A→1S2 | ϵ

B→0B3 | A |ϵ

Then the CFG that accepts S is T.