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# Is ETM co Turing recognizable?

## Is ETM co Turing recognizable?

ETM is not Turing-recognizable. Rice’s Theorem: Every nontrivial property of the Turing-recognizable languages is undecidable.

## What does co Turing recognizable mean?

Intuitively, if a language is co-Turing-recognizable, it means that there is a computer program that, given a string not in the language, will eventually confirm that the string is not in the language. It might loop infinitely if the string is indeed within the language, though.

## Is a CFG Turing recognizable?

If both CFGs or neither CFG can generate si, then TM moves on to consider the next string in string order. Otherwise, exactly one of the CFGs generates the string and the other CFG does not, so the CFGs are not equivalent, and the TM accepts. Thus, D is Turing- recognizable.

## What are Turing recognizable languages?

A language is “Turing-Recognizable” iff there exists a Turing Machine such that. when encountering a string in that language, the machine terminates and accepts that string; when encountering a string not in that language, the machine either terminates and rejects that string or doesn’t terminate at all.

## Is halt TM recognizable?

There is no way to decide whether a TM will accept or eventually terminate. and HALT are recognizable. We can always run a TM on a string w and accept if that TM accepts or halts.

## Which language is decidable?

Definition: A language for which membership can be decided by an algorithm that halts on all inputs in a finite number of steps — equivalently, can be recognized by a Turing machine that halts for all inputs. Also known as recursive language, totally decidable language.

## Does Undecidable mean unrecognizable?

2 Answers. No. It can be recognizable (those whose language is recursively enumerable but not recursive) or unrecognizable (those whose language is not even recursively enumerable).

## Will halt on every input?

In computability theory, a machine that always halts, also called a decider or a total Turing machine, is a Turing machine that eventually halts for every input. Because it always halts, such a machine is able to decide whether a given string is a member of a formal language.

## Is ATM complement decidable?

Corollary 4.23: ATM is Turing-recognizable but not decidable, so its complement ATM is NOT Turing-recognizable.