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Problem Detail: Rice’s theorem tell us that the only semantic properties of Turing Machines (i.e. the properties of the function computed by the machine) that we can decide are the two trivial properties (i.e. always true and always false). But there Read More …

Problem Detail: I read a quotation attributed to Sheila Greibach that says that the intersection of two context free grammars is recursively enumerable. I could not, however, find a citation for this quotation (and searching has failed to turn up a Read More …

Problem Detail: We have operator and operands, function and formal arguments. Is the difference purely lexical (we use alphanumerics for funciton identifiers but identify operators with special characters, e.g. “+” and “>=”) or it is syntactical, like I guessed here f(a,b) Read More …

Problem Detail: I’m having a problem understanding this conversion. Let’s say we have a CFL like this: $ { a^nb^m : n > m } $ A final state acceptance PDA for this language would push $A$ symbols in the stack Read More …

Problem Detail: I know from Sedgewick’s book on algorithms that the max depth of any node x from a set of N nodes is at most log2(N) applying the algorithm(which says to put the shorter tree beneath to avoid tall trees) Read More …

Problem Detail: Are there undecidable properties of linear bounded automata (avoiding the empty set language trick)? What about for a deterministic finite automaton? (put aside intractability). I would like to get an example (if possible) of an undecidable problem that is Read More …

Problem Detail: I have the following problem: Define the keyed function F as follows: On input k ∈ {0, 1}$^n$ and x ∈ {0, 1}$^n$ , Fk(x) = k ⊕ x.Rigorously prove that F is not a pseudorandom function. How do Read More …

Problem Detail: I would like to create a deterministic finite state automaton (DFA) M=(Q, Σ, δ, q0, F) that is accepting the language generated by the following regular grammar (RG) G=(N, Σ, P, S). In short I want to convert RG Read More …