Miriam M. Müller: A Spectre is Haunting Arabia: How the Germans Brought Their Communism to Yemen. transcript Verlag, 30.11.2015. ISBN 9783839432259Teoksen verkkoversio Viitattu 7.8.2018. (englanti)
Rainer Grote, Tilmann Röder: Constitutionalism in Islamic Countries: Between Upheaval and Continuity. OUP USA, 16.2.2012. ISBN 9780199759880Teoksen verkkoversio Viitattu 6.8.2018. (englanti)