Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Following problem is decidable:

Given a context-free grammar $G$, is $L(G) = \varnothing$?

Following problem is undecidable:

Given a context-free grammar $G$, is $L(G) = A^{\ast}$?

Is there a characterization of context-free languages $M$ with decidable equality $L(G) = M$?

share|cite|improve this question
The general equivalence problem on CFL's is undecidable, but I guess you want a subset of all CFL's for which the equivalence problem is decidable? – sxd Aug 11 '11 at 1:10
@Dimitri: I'd like a description of the set $X$ of languages such that $M \in X$ iff it is decidable given any CFG $G$ (not neccessarily from $X$) if $L(G) = M$. – sdcvvc Aug 11 '11 at 6:29
Crossposted to cstheory. – sdcvvc Aug 14 '11 at 11:52
up vote 0 down vote accepted

Question was answered at cstheory.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.