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Unformatted text preview: COT 5310 Assignment 7 Key, Fall 2007 1. Present the description of a PDA (in words) that accepts L A (see page 253 of Notes). You may assume that [ i ] is a single symbol. A PCP instance over consists of two vectors x, y over where  x  =  y  = n . Let I = { 1 , . . . , n } and be disjoint from (we use just i instead of [ i ] to denote the index). L A is the language generated by the grammar A x i A i  x i i for i I over the alphabet = I . So L A = braceleftbig x i 1 x i 2 . . . x i k 1 x i k i k i k 1 . . . i 2 i 1 : 1 i j n for 1 j k and i j I and x i j bracerightbig . To make a PDA that accepts this language, use = I as the stack symbols, with Z as the bottom of stack marker. Well push symbols until we reach an element i I . Then well pop ( x i ) R from the top of the stack and repeat. If we run out of input and have an empty stack, then were in L A . 1) Read in elements of and push them onto the stack. When encountering some i I , push it onto the stack and move to step 2). 2) Pop i from the stack and check if w i R is on top of the stack. If it isnt, were not in L A so transition to a nonaccepting state r ). If w i R is on top, and the bottom of stack symbol is exposed, transition to an accepting state a )....
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This note was uploaded on 07/14/2011 for the course COT 5310 taught by Professor Staff during the Spring '08 term at University of Central Florida.
 Spring '08
 Staff

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