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February 1971 (vol. 20 no. 2)
pp. 149-153
A regular expression is called unambiguous if every tape in the event can be generated from the expression in one way only. The flow-graph technique for constructing an expression is shown to preserve ambiguities of the graph, and thus, if the graph is that of a deterministic automaton, the expression is unambiguous. A procedure for generating a nondeterministic automaton which preserves the ambiguities of the given regular expression is described. Finally, a procedure for testing whether a given expression is ambiguous is given.
Index Terms:
Ambiguity of regular expressions, decidability of ambiguity, flow-graph algorithm, preservation of ambiguity of graphs, preservation of ambiguity of regular expressions.
Citation:
R. Book, S. Even, S. Greibach, G. Ott, "Ambiguity in Graphs and Expressions," IEEE Transactions on Computers, vol. 20, no. 2, pp. 149-153, Feb. 1971, doi:10.1109/T-C.1971.223204
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