Gaston Leroux (2016). “The Phantom of the Opera & The Mystery of the Yellow Room (Mystery Classics): The Ultimate Gothic Romance Mystery and One of the First Locked-Room Crime Mysteries”, p.42, e-artnow
Gaston Leroux (2016). “The Phantom of the Opera & The Mystery of the Yellow Room (Mystery Classics): The Ultimate Gothic Romance Mystery and One of the First Locked-Room Crime Mysteries”, p.10, e-artnow