Author: ignougroup

Problem Detail: Let $A$ and $B$ be two languages. If $A le_{m} B$ ( reducible by mapping ) then I know that if $B$ is decidable so is $A$ and if $B$ is recognizable so is $A$. And if $A le_{T} Read More …

Problem Detail: I wonder if the following two substitutions are correct: $$(x,y)[x:=y] = (y,y)$$ $$ lambda y. (x,y) [x:=y] = lambda z.(y,z)$$ They are what I understand from http://en.wikipedia.org/wiki/Lambda_calculus#Substitution. Although I can follow the rules there mechanically, I wonder why there Read More …

Problem Detail: I want to know the difference between these three languages and it would be great if you would give some examples as well, thank you. 🙂 Asked By : hackhan Answered By : Yuval Filmus An alphabet $Sigma$ is a finite Read More …

Problem Detail: Let $n$ be the number of strings which are sorted in lexicographical order and stored in a balanced binary search tree. You are provided with a prefix $x$ of which $M$ strings have the prefix $x$. I have devised Read More …

Problem Detail: making exercises to prepare a test I’m having problems to understand 2 questions, the questions are: how many are the leafs of a decisional tree associated to any algorithm for the search problem in a ordered set? for this Read More …

Problem Detail: So, I remember the professor saying that SAT does not reduce to QBF (Quantifier Boolean Formula) $QBF ::= prop|-QBF|(QBFoQBF)|exists pQBF |forall pQBF$ So, I guess this is not NP, since solving a QBF could grow exponentially. However, $P subseteq Read More …

Problem Detail: I know that maximum independent set on cubic triangle-free graphs is NP-complete. Is it still NP-complete in case we require the independent set to be of size exactly $|V|/2$? Basiclly, YES instance of independent set problem on cubic triangle-free Read More …

Problem Detail: I have started reading on algorithmic complexity for my thesis work. Already have studied on Polynomial time reducibility, NP-Complete, NP-Hard. Now trying to prove NP completeness of some of the classical problems. I have started with 3-SAT problem. 3-SAT Read More …

Problem Detail: I know that in general it is undecidable whether two context free grammars generate the same language, but I have to do this exercise and I am finding myself somewhat stuck: G1: S->e|aB|bA B->bS|aBB A->aS|bAA G2: S->e|aSb|bSa|SS I tried Read More …