I forgot to mention: With regard to the dangerous practice of using "==" (as in your `elem` example) on Double, every computer scientist or programmer should read the following paper at some point in their training: David Goldberg, "What every computer scientist should know about floating-point arithmetic". ACM Computing Survey Volume 23 , Issue 1 (March 1991) Pages: 5 - 48. http://portal.acm.org/citation.cfm?id=103163 --KW 8-) -- Keith Wansbrough <kw217@cl.cam.ac.uk> http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory.