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Unformatted text preview: FLAC Assignment 8 Exercise 1. Show that the question of whether a Turing Machine halts on a blank tape is undecidable. Exercise 2. A queue automaton is like a pushdown automaton except that the stack is replacd by a queue. A queue is a tape allowing symbols to be written only on the left-hand end and read only at the right-hand end. Each write operation (we’ll call it a push ) adds a symbol to the left-hand end of the queue and each read operation (we’ll call it a pull ) reads and removes a symbol at the hand-hand end. As with a PDA, the input is placed on a seperate read-only input tape, and the head on the input tape can move only from left to right. The input tape contains a cell with a blank symbol following the input, so that the end of the input can be detected. A queue automaton accepts its input by entering a special accept state at any time. Show that the question of whether a deterministic queue automaton (DQA) halts on a tape is undecidable. (Hint: Show that a language can be recognized by a DQA iff the languageis undecidable....
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This note was uploaded on 02/29/2012 for the course CS 15-453 taught by Professor Edmundm.clarke during the Spring '09 term at Carnegie Mellon.
- Spring '09