no. 1
Strong iterative pairs and the regularity of context-free languages
RAIRO. Informatique théorique, Tome 19 (1985) no. 1, pp. 43-56 
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     title = {Strong iterative pairs and the regularity of context-free languages},
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     year = {1985},
     publisher = {EDP Sciences},
     volume = {19},
     number = {1},
     mrnumber = {795771},
     zbl = {0601.68053},
     language = {en},
     url = {https://www.numdam.org/item/ITA_1985__19_1_43_0/}
}
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Ehrenfeucht, A.; Rozenberg, G. Strong iterative pairs and the regularity of context-free languages. RAIRO. Informatique théorique, Tome 19 (1985) no. 1, pp. 43-56. https://www.numdam.org/item/ITA_1985__19_1_43_0/

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