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Hayashi, Mitsuo; Hori, Tadao (1998). "The effects of a 20-min nap before post-lunch dip". Psychiatry and Clinical Neurosciences. 52 (2). ss. 203-4. doi:10.1111/j.1440-1819.1998.tb01031.x. PMID9628152.
Lahl, Olaf; Wispel, Christiane; Willigens, Bernadette; Pietrowsky, Reinhard (2008). "An ultra short episode of sleep is sufficient to promote declarative memory performance". Journal of Sleep Research. 17 (1). ss. 3-10. doi:10.1111/j.1365-2869.2008.00622.x. PMID18275549.