I have been starting to learn about CFGs and PDAs and have gotten familiar with the simple stuff. I have been able to construct CFGs for simple languages but this question is more specific:
$\lbrace 0^a1^b2^c3^d4^e5^f |a,b,c,d,e,f \geq 0$ and $a+b=d+e\rbrace$.
My thought process has only gone so far. I see that if you add a 0 you must add a 3 or 4, the same is if you add a 1. And for adding a 3 or 4 the case is very similar. My biggest troubles are due to the characters that lay between the pairs of 0s,1s,3s and 4s. I haven't been able to produce a serious attempt yet, but will post it as an edit if I do. Any help would be appreciated.
Edit: Here is a possible solution I have come to:
$B\rightarrow B5|\epsilon $