SUTTON, David, ed. (1998) UNSPECIFIED Churchill Livingstone, s.l. ISBN 978 044 307 108 X

SUTTON, David, ed. (1998) UNSPECIFIED Churchill Livingstone, s.l. ISBN 978 044 307 108 X

DAKE, LP (1998) UNSPECIFIED Elsevier, Amsterdam. ISBN 978 044 441 830 X

GAWAIN, Shakti and KING, Lawrel (1998) Living in the Light A guide to personal transformation. Nataraj Publishing, Canada. ISBN 978 157 731 046 2