User Marzio De Biasi

45 votes

Accepted

What is the smallest Turing machine where it is unknown if it halts or not?

answered Feb 11, 2014 at 8:18

37 votes

Accepted

Is this variation of TQBF still PSPACE-complete?

answered Sep 3, 2014 at 18:17

31 votes

Accepted

Turing Machine restrictions that render halting decidable

answered May 12, 2016 at 13:32

29 votes

A simple decision problem whose decidability is not known

answered Sep 4, 2013 at 6:55

27 votes

Techniques for showing that problem is in hardness "limbo"

answered Feb 6, 2014 at 7:54

26 votes

Accepted

What is the "nearest" problem to the Collatz conjecture that has been successfully resolved?

answered Jun 2, 2012 at 9:55

25 votes

How much time to recognize palindromes in logarithmic space?

answered Mar 3, 2014 at 13:41

21 votes

Accepted

Is the longest trail problem easier than the longest path problem?

answered Jan 22, 2014 at 16:18

21 votes

Accepted

Dark Integers: General Purpose Computations on Internet Routers

answered May 25, 2011 at 8:16

21 votes

Direct SAT to 3-SAT reduction

answered Jul 3, 2011 at 18:27

20 votes

Accepted

Intersection of languages in NP

answered Dec 10, 2015 at 10:43

19 votes

Accepted

Are DPDAs without a $\epsilon$ moves as powerful as DPDAs with them?

answered Aug 14, 2015 at 23:35

19 votes

Accepted

The complexity of counting simple paths in a directed graph

answered Sep 7, 2014 at 22:17

18 votes

Golden ratio or Pi in the running time

answered Jan 8, 2013 at 16:46

17 votes

Accepted

Co-NP-completeness of minimal TSP tour?

answered Jan 10, 2014 at 17:20

17 votes

Easy problems with hard counting versions

answered Oct 20, 2016 at 12:55

17 votes

Accepted

Algorithm whose running time depends on P vs. NP

answered Oct 19, 2018 at 17:00

16 votes

Accepted

Is it possible to find if a sequence exists in polynomial time in the following problem?

answered Feb 3, 2011 at 1:44

15 votes

What are the popular science books that inspire TCS?

answered Sep 13, 2013 at 21:46

15 votes

What is the simplest computational model for which the emptiness problem is undecidable?

answered Mar 25, 2014 at 9:00

14 votes

Accepted

Natural complete problems in higher levels of the $\mathsf{W}$-hierarchy

answered Sep 12, 2014 at 7:51

14 votes

Is it decidable to determine if a given shape can tile the plane?

answered Sep 15, 2015 at 15:31

14 votes

Curious about computer-assisted NP-completeness proofs

answered Feb 2, 2015 at 15:38

14 votes

Accepted

How hard is binary Sudoku puzzle?

answered Mar 23, 2013 at 20:28

14 votes

Accepted

Is every recursive language recognized by a mortal Turing machine?

answered Feb 15, 2014 at 19:36

14 votes

Accepted

Is there any known NP-Complete (or NP-Intermediate) problem in sublinear nondeterministic space?

answered May 5, 2012 at 11:16

14 votes

What's the simplest noncontroversial 2-state universal Turing machine?

answered Feb 14, 2012 at 18:33

14 votes

Beautiful results in TCS

answered Feb 28, 2012 at 14:48

13 votes

Oblivious Turing Machine emulation lower bound

answered Mar 12, 2012 at 0:25

12 votes

What is the counting complexity of random 2-SAT?

answered Mar 16, 2012 at 23:30

Stack Exchange Network

261 Answers

What is the smallest Turing machine where it is unknown if it halts or not?

Is this variation of TQBF still PSPACE-complete?

Turing Machine restrictions that render halting decidable

A simple decision problem whose decidability is not known

Techniques for showing that problem is in hardness "limbo"

What is the "nearest" problem to the Collatz conjecture that has been successfully resolved?

How much time to recognize palindromes in logarithmic space?

Is the longest trail problem easier than the longest path problem?

Dark Integers: General Purpose Computations on Internet Routers

Direct SAT to 3-SAT reduction

Intersection of languages in NP

Are DPDAs without a $\epsilon$ moves as powerful as DPDAs with them?

The complexity of counting simple paths in a directed graph

Golden ratio or Pi in the running time

Co-NP-completeness of minimal TSP tour?

Easy problems with hard counting versions

Algorithm whose running time depends on P vs. NP

Is it possible to find if a sequence exists in polynomial time in the following problem?

What are the popular science books that inspire TCS?

What is the simplest computational model for which the emptiness problem is undecidable?

Natural complete problems in higher levels of the $\mathsf{W}$-hierarchy

Is it decidable to determine if a given shape can tile the plane?

Curious about computer-assisted NP-completeness proofs

How hard is binary Sudoku puzzle?

Is every recursive language recognized by a mortal Turing machine?

Is there any known NP-Complete (or NP-Intermediate) problem in sublinear nondeterministic space?

What's the simplest noncontroversial 2-state universal Turing machine?

Beautiful results in TCS

Oblivious Turing Machine emulation lower bound

What is the counting complexity of random 2-SAT?