Pham, D. “Sur La Syntaxe d’un Langage De sélection: On the Syntax of a Selection Language”. Anal. Numér. Théor. Approx., vol. 6, no. 2, Aug. 1977, pp. 177-83, https://ictp.acad.ro/jnaat/journal/article/view/1977-vol6-no2-art10.