Issue No.02 - February (1971 vol.20)
R. Book , IEEE
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.
Ambiguity of regular expressions, decidability of ambiguity, flow-graph algorithm, preservation of ambiguity of graphs, preservation of ambiguity of regular expressions.
S. Even, R. Book, G. Ott, "Ambiguity in Graphs and Expressions", IEEE Transactions on Computers, vol.20, no. 2, pp. 149-153, February 1971, doi:10.1109/T-C.1971.223204