M. Schmitz; G. Helou; P. Dubois; C. LaGue; B. Madore; H. G. Corwin Jr.; S. Lesteven (1995). «NED and SIMBAD Conventions for Bibliographic Reference Coding». I Daniel Egret; Miguel A. Albrecht. Information & On-Line Data in Astronomy. Kluwer Academic Publishers. ISBN0-7923-3659-3. Henta 22. juni 2011.