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\bibitem[{B{\~A}{\textparagraph}hm \& Tronci}(1987)]{BAPhm+Tronci1987} Corrado B{\~A}{\textparagraph}hm, and Enrico Tronci. "X-Separability and Left-Invertibility in lambda-calculus." In \textit{Symposium on Logic in Computer Science (LICS)}, 320--328. Ithaca, New York, USA: IEEE Computer Society, 1987.

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