# Intersection between context-free and context-sensitive language decidability [closed]

I'm trying to find a formal proof of the following fact:

Given a context-free language, say $L_1$, and a context-sensitive language, say $L_2$, it is NOT decidable if their intersection is empty ($L_1 \cap L_2 = \emptyset$)

Some suggestions for the proof? Thanks

• (It's also undecidable for a single context-sensitive language i.e. $L=\emptyset$) – sdcvvc Dec 26 '13 at 17:42