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\bibitem[{B{\~A}{\textparagraph}hm \& Tronci}(1991)]{BAPhm+Tronci1991} Corrado B{\~A}{\textparagraph}hm, and Enrico Tronci. "About Systems of Equations, X-Separability, and Left-Invertibility in the lambda-Calculus." \textit{Inf. Comput.} 90, no. 1 (1991): 1--32. DOI: 10.1016/0890-5401(91)90057-9.

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