Ambiguity in Graphs and Expressions
Robert T. Book, Shimon Even, Sheila A. Greibach, Gene Ott · IEEE Transactions on Computers · 1971
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.