Doubt on decidability

Question

I have a doubt regarding the dilemma of semidecidable and undecidable..

We have 8 standard properties and considering each class of language:

a) Membership

b) Finiteness

c) Emptiness

d) Ambiguity

e) Regularity

f) Equivalence

g) Kleene's Closureness

h) Disjointedness..

In general if for a given class of language one of the above mentioned properties fail , then do we say the problem is semidecidable or undecidable for a class of language under that particular operation??

@Arjun sir,plz help me resolving this doubt..It would be helpful of other aspirants as well..

Comments

Maybe, This can help you 

http://gatecse.in/grammar-decidable-and-undecidable-problems/

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In general if for a given class of language one of the above mentioned properties fail , then do we say the problem is semidecidable or undecidable for a class of language under that particular operation??
 

If we have to say so, we have to prove why. Actually Rice's theorem says the same for R.E. languages  which makes what you asked true for R.E. sets. Be it any property- as long as it is non-trivial, it is undecidable for r.e. sets.

For other sets, some are undecidable, some are not. May be you can collect all such ones. I have given the properties for Context-Free here.

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Can't we prove it through examples Sir? By taking for various classes of Languages respectively Sir.

How that is done Sir? May be not all examples prove or fall in the given criteria Sir.