ISBN 978-0-415-14416-2. Retrieved 31 May 2011. ↑ Trample, Christopher "A Maiden Guards the Door: Symbolism and Meaning in Mythology" (http://www.public.iastate.edu/~ctrampel/Trampel_Mythology_Journal_Format2.pdf%5Bpermanent+dead+link%5D), accessed 02.09.2013 ↑ Jeffrey H. Tigay (November 2002).