found: Franse figuren, 1959:t.p. (P. Geyl)
found: Debates with historians, 1962, c1955:t.p. (Pieter Geyl)
found: LC data base, 3-16-89(hdg.: Geyl, Pieter, 1887-1966; usage: Pieter Geyl; P. Geyl)
found: BL database 13 Mar. 2009(hdg.: Geyl, Pieter Catharinus Arie)
found: Catalogus Professorum Academiae Rheno-Traiectinae, viewed August 17, 2024(P.C.A. Geyl ; professor of general history and national history of the modern era, 1936-1942; professor of general history and national history, 1945-1958 ; before was a professor at the University of London ; born 15 December 1887 in Dordrecht, died 31 December 1966 in Utrecht) - https://profs.library.uu.nl/index.php/profrec/getprofdata/667/49/149/0 found: Nederlandse Thesaurus van Auteursnamen (NTA), viewed August 17, 2024(Geyl, P. (Pieter Catharinus Arie) ; variant name: Geijl, P. ; also published under the pseudonym A. v. d. Merwe)
found: Katalog der Deutschen Nationalbibliothek, viewed August 17, 2024(Geyl, Pieter ; variant names: Geyl, Pieter C.; Geyl, Pieter Cathariens Arie; Geijl, Pieter) - https://d-nb.info/gnd/119252171
