Stone, David. Sybil GordonArhivirano 2009-10-01 na Wayback Machine-u at the Who Was Who in the D'Oyly Carte Opera Company website, 11 July 2002. Retrieved 8 November 2009
diamond.boisestate.edu
Stone, David. Sybil EversArhivirano 2014-10-15 na Wayback Machine-u at the Who Was Who in the D'Oyly Carte Opera Company website, 28 January 2002. Retrieved 8 November 2009
Stone, David. Sybil GordonArhivirano 2009-10-01 na Wayback Machine-u at the Who Was Who in the D'Oyly Carte Opera Company website, 11 July 2002. Retrieved 8 November 2009
Stone, David. Sybil EversArhivirano 2014-10-15 na Wayback Machine-u at the Who Was Who in the D'Oyly Carte Opera Company website, 28 January 2002. Retrieved 8 November 2009