Let L1 be a language generated by a CFG. Let L2 be a language generated by a regular grammar. Is L1 = L2 ?
Is the above problem decidable or undecidable ?
If L1 = L2 then L1 $\cap$ L2' = $\phi$
So the above problem can be written as
CFL $\cap$ RL = $\phi$ or CFL = $\phi$ which is decidable.
So the answer should be decidable according to me but my professor marked it wrong saying it's undecidable
Where am I going wrong ?