Russ Hudson (Hudson, Russ)

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  Discovering Your Personality Type: The Essential Introduction to the Enneagram
  by Russ Hudson, Don Richard Riso
  Softcover, Houghton Mifflin, ISBN 061821903X (0-618-21903-X)
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  Personality Types: Using the Enneagram for Self-Discovery
  by Russ Hudson, Don Richard Riso
  Softcover, Houghton Mifflin, ISBN 0395798671 (0-395-79867-1)
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  The Riso-Hudson Enneagram Type Indicator (Rheti, Version 2.5)
  by Russ Hudson, Don Richard Riso
  Softcover, Enneagram Inst, ISBN 0970382405 (0-9703824-0-5)
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  Understanding the Enneagram: The Practical Guide to Personality Types
  by Russ Hudson, Don Richard Riso
  Softcover, Houghton Mifflin, ISBN 0618004157 (0-618-00415-7)
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  via
  The Wisdom of the Enneagram: The Complete Guide to Psychological and Spiritual Growth for the Nine Personality Types
  by Russ Hudson, Don Richard Riso
  Softcover, Bantam Dell Pub Group, ISBN 0553378201 (0-553-37820-1)