Hellinger, Bert (2000). Love's hidden symmetry : what makes love work in relationships. Zeig, Tucker & Theisen Pub. ISBN978-1-891944-66-6. OCLC44026482.
Sheldrake, Rupert (2012). The Presence of the Past : Morphic Resonance and the Memory of Nature. Inner Traditions International, Limited. ISBN978-1-59477-707-3. OCLC1085226451.