Explicit use of et al. in: |author= (help) Karol, P.J.; Nakahara, H.; Petley, B.W.; Vogt, E. (2003). "Karol et al" (PDF). Pure Appl. Chem. 75 (10): 1601–1611...
First Hundred Years. London: Capital Transport. ISBN 978-1-85414-305-1. Karol, Eitan (2007). Charles Holden: Architect. Shaun Tyas. ISBN 978-1-900289-81-8...