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Química oculta
Casas, Alberto. El lado oscuro del universo / A. Casas. – Madrid: CSIC, 2010.
El lado oscuro del universo
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Case-Book of Astral Projection
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Events on the Threshold of the After-Life
Crookall, Robert. Las técnicas de la proyección astral / R. Crookall. – Buenos Aires: Ediciones Lidiun, 1990.
Las técnicas de la proyección astral
Crookall, Robert. More Astral Projections / R. Crookall. – London: Aquarian Press, 1964.
More Astral Projections
Crookall, Robert. The Study and Practice of Astral Projection. New Jersey: Cita del Press. 1960.
The Study and Practice of Astral Projection
Crookall, Robert. The Mechanisms of Astral Projection / R. Crookall. – Moradabad (India): Darshana International, 1968.
The Mechanisms of Astral Projection
Crookall, Robert. The Supreme Adventure / R. Crookall. – James Clarke & Co. Limited, 1961.
The Supreme Adventure
Crookall, Robert. What Happens when you Die / R. Crookall. – Gerrard cross: Colin Smythe, 1978.
What Happens when you Die