^Alexander M. Schenker. 1993. "Proto-Slavonic," The Slavonic Languages. (Routledge). Pp. 60-121. Pg. 60: "[The] distinction between dialect and language being blurred, there can be no unanimity on this issue in all instances..." C.F. Voegelin and F.M. Voegelin. 1977. Classification and Index of the World's Languages (Elsevier). Pg. 311, "In terms of immediate mutual intelligibility, the East Slavic zone is a single language." Bernard Comrie. 1981. The Languages of the Soviet Union (Cambridge). Pg. 145-146: "The three East Slavonic languages are very close to one another, with very high rates of mutual intelligibility...The separation of Russian, Ukrainian, and Belorussian as distinct languages is relatively recent...Many Ukrainians in fact speak a mixture of Ukrainian and Russian, finding it difficult to keep the two languages apart...
^Beswick, Jaine (2005). “Linguistic homogeneity in Galician and Portuguese borderland communities”. Estudios de Sociolingüística6 (1): 39–64.
^Bø, I (1976). “Ungdom og naboland : en undersøkelse av skolens og fjernsynets betydning for nabospråkforståelsen.”. Rogalandsforskning4.
^GAVILANES LASO, J. L. (1996) Algunas consideraciones sobre la inteligibilidad mutua hispano-portuguesa In: Actas del Congreso Internacional Luso-Español de Lengua y Cultura en la Frontera, Cáceres, Universidad de Extremadura, 175-187.