Source: https://www.researchgate.net/profile/Lalina_Coulange/publication/242565184_EVOLUTION_DU_PASSAGE_ARITHMETIQUE-ALGEBRE_DANS_LES_MANUELS_ET_LES_PROGRAMMES_DU_20_EME_SIECLE_CONTRAINTES_ET_ESPACES_DE_LIBERTE_POUR_LE_PROFESSEUR/links/53fa0ad70cf27c365ceb88f9.pdf