In: Computer Science
Please write an example of a language that is
Turing-decidable but not Context-Free. You can just state what the
language is; no need to give a full TM algorithm for
it.
1b) Please write an example of a language that is not Turing-decidable. You can just state what the language is; no need to give a full TM algorithm for it.
Undecidable Problems
A problem is undecidable if there is no Turing machine which will
always halt in finite amount of time to give answer as ‘yes’ or
‘no’. An undecidable problem has no algorithm to determine the
answer for a given input.
Examples
Note: Two popular undecidable problems are halting problem
of TM and PCP (Post Correspondence Problem). Semi-decidable
Problems
A semi-decidable problem is subset of undecidable problems for
which Turing machine will always halt in finite amount of time for
answer as ‘yes’ and may or may not halt for answer as ‘no’.
Relationship between semi-decidable and decidable problem has been
shown in