1. US 1,506,316. Assigned to Pharma-Chemical Corporation by Eugene A. Markush. Filed January 9, 1923; issued August 26, 1924
2. Ex parte Markush. 340 O.G. 839, 1924
3. http://www.derwent.com/profile/history.html
4. Survey of Chemical Notafion Systems;Hunsberger,1964
5. Chemical substructure searching––industrial applications and commercial systems;Almond;Drexel Library Quart.,1982