Are there any open problems concerning decidability?
46430
A simple decision problem whose decidability is not known
121575
Meet-in-the-middle with checking complexity
119888
Is it possible to convert $\forall$ quantifiers to $\exists$ quantifiers without negation?
49893
"Are there finitely or infinitely many Fermat primes?": decidable?
93040
$f$ is surjective iff it has a right inverse: using the axiom of choice and errors in ProofWiki
45663
What are some major open problems in Galois theory?
94703
Time complexity and optimality
77189
Prolog successor notation yields incomplete result and infinite loop
6535
Proof of for-all / there-exists "negation"?
79407
How to solve ~(P → Q) : P & ~Q by natural deduction?
18383
List of ways to tell if degree sequence is impossible for a simple graph
20190
Counter Proof to determinism?
98559
subtlety of self-defined function and its evaluation
67541
When does "X is NP-complete" imply "#X is #P-complete"?
56528
On the proof of existence and uniqueness of radix representation
143573
Problem (1.8) A Path to Combinatorics Solution Verification.
68882
Path to Combinatorics Problem [$1.11$]