Xiru Zhang Jacquelyn S. Fetrow William A. Rennie David L. Waltz George Berg Automatic Derivation of Substructures Yields Novel Structural Building Blocks in Globular Proteins. 438-446 1993 conf/ismb/1993 ISMB db/conf/ismb/ismb1993.html#ZhangFRWB93 http://www.aaai.org/Library/ISMB/1993/ismb93-051.php