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Problem Detail: In a course of computer science it is common to study the hierarchy of formal languages, grammars, automata and Turing machines. I wonder what is the relationship of these objects with formal systems. For example, lambda calculus is said Read More …

Problem Detail: If A and B are Turing recognizable, is A – B Turing recognizable? I think that A – B would be Turing recognizable because they’re both in the space of Turing recognizability. For example, if A is context free Read More …

Problem Detail: Robert Sedgewick, at his Algorithms – Part 1 course in Coursera, states that people usually misunderstand the big-O notation when using it to show the order of growth of algorithms. Instead, he advocates for the tilde notation. I understand Read More …

Problem Detail: I’ve been trying to efficiently solve this problem : given a integer p > 0 and a directed graph whose nodes are 0, …, N-1, enumerate (not simply count) all the paths (not necessarily elementary) from a node i Read More …

Problem Detail: I’m learning Dynamic Programming (By myself) and in the textbook there is this question: Given two undirected graphs $G_1=(V,E_1)$ and $G_2=(V,E_2)$ over the same set of Vertices $V$ and a weight function $w: E_1 cup E_2 rightarrow mathbb{R}$, let Read More …

Problem Detail: In class, we were given the following problem: We are given a directed graph G = (V, E) on which each edge (u, v) ∈ E has an associated value r(u, v) which is a real number in the Read More …

Problem Detail: How can I prove that non-regular languages are closed under concatenation using only the non-regularity of $L={a^nb^n|nge1}$ ? Asked By : TT8 Answered By : David Richerby You can’t prove it because it isn’t true: the class of non-regular languages isn’t Read More …

Problem Detail: I am new to StackExchange, and I already made the mistake of posting a new question as a response to a previous question. Here, I rewrote my question more clearly and separately. I am trying to store an existing Read More …

Problem Detail: True or false: An intersection of a Turing-recognizable and a regular language is always Turing-decidable. This was asked on a practice test and the answer is False. Why? I thought regular languages were a subset of decidable languages. So Read More …

Problem Detail: Assume we have a simple language that consists of the terms: $mathtt{true}$ $mathtt{false}$ if $t_1,t_2,t_3$ are terms then so is $mathtt{if}: t_1 :mathtt{then}: t_2 :mathtt{else}: t_3$ Now assume the following logical evaluation rules: $$ begin{gather*} dfrac{} {mathtt{if}: mathtt{true} :mathtt{then}: Read More …