@book { KompetenzFunktionVariationCompetenciaFuncinVariacin,
    title = "Kompetenz – Funktion – Variation / Competencia – Función – Variación",
    author = "Gerda {Hassler} and Thomas {Stehl}",
    year = "2017",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/b11258",
    url = "https://www.peterlang.com/document/1050058"
}