FAQ Database Discussion Community


NP and 3-SAT and One Facts

computation-theory,turing-machines,np-complete,np,decidable
any expert could help me why this sentence is True? if L ∈ NP and L ≤p 3−SAT (i.e: reduce L to 3-SAT in poly time) then L is NP-Complete. ...

Is equality decidable on any coinductive type?

coq,decidable,coinduction
this is my first post, apologies if it I have made mistakes. I suspect that, in Coq, coinductive types like Stream do not have decidable equality. That is, given two streams s and t, it is not possible identify whether s=t or ~(s=t). I suspect that this is true of...

P is undecidable and not semidecidable, Q is undecidable and semidecidable and P ⊂ Q

formal-languages,decidable
My problem: Define two sets P and Q of words (that is, two problems) such that: P is undecidable and not semidecidable, Q is undecidable and semidecidable and P ⊂ Q