Apel, Willi, ed. The Harvard Dictionary of Music. 2nd ed.
Cambridge: Belknap Press of
Harvard University Press,
1969. S.v. "Virtuoso."
Randel, Don Michael, ed. The New Harvard Dictionary of Music.
Cambridge: Belknap Press
of Harvard University Press,
1986. S.v. "Virtuoso."
Slonimsky, Nicholas, rev. Baker's Biographical Dictionary of
Musicians. 8th ed. New York:
Schirmer, 1992. S.v.
"Nordgren, Pehr Henrik."