(Shaders found from Siggraph 1991 Course 21)
This source is as it is found on p. 103 of course 21 Siggraph 1991. To be honest, I could never to get this shader to work as is.
A more generalized version with explainations can be found at
Siblings: BMRTShaders AKShaders DPShaders DWShaders EMShaders FGShaders FSShaders IDShaders DWShaders KMShaders JBUMShaders JMShaders LGShaders LCShaders MBShaders MRShaders MKShaders PQShaders RCShaders SHWShaders SWShaders XMBShaders SIG2000 SIG2001 TLShaders
RenderMan is a registered trademark of Pixar. The RenderMan Repository is maintained by Pixar's RenderMan Products Group