no. 1
On equality sets of morphisms in topological free monoids
RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 25 (1991) no. 1, pp. 39-42. 
@article{ITA_1991__25_1_39_0,
     author = {Fory\'s, Wit},
     title = {On equality sets of morphisms in topological free monoids},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {39--42},
     publisher = {EDP-Sciences},
     volume = {25},
     number = {1},
     year = {1991},
     mrnumber = {1104409},
     zbl = {0721.68034},
     language = {en},
     url = {http://archive.numdam.org/item/ITA_1991__25_1_39_0/}
}
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VL  - 25
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Foryś, Wit. On equality sets of morphisms in topological free monoids. RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 25 (1991) no. 1, pp. 39-42. http://archive.numdam.org/item/ITA_1991__25_1_39_0/

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4. Ch. Reutenauer, Une topologie du monoide libre, Semigroup Forum, 1979, 18. | MR | Zbl