@book { ProfessionalTrainingofSingersandTeachersofSinging,
    title = "Professional Training of Singers and Teachers of Singing",
    author = "Jeffrey {Treganza}",
    year = "2007",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1103729"
}