In this lecture by Shai Simonson : https://youtu.be/77OG6ziPMu4
At 33:04 he mentions that "A = CFL that does not accept $\sum^*$ " is Undecidable.
Also, we already know that "A' = CFL that accept $\sum ^*$ " is Undecidable as well.
so if A and A' both are Recursively Enumerable sets, then wouldn't that make A a recursive set ?
First of all, congratulations!
Please elucidate this really important...