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Hartvig, P. L.; Kjelsberg, E. (2009). “Penrose's Law revisited: The relationship between mental institution beds, prison population and crime rate”. Nordic Journal of Psychiatry63 (1): 51–56. doi:10.1080/08039480802298697. hdl:10852/27918. PMID18985517.
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Hartvig, P. L.; Kjelsberg, E. (2009). “Penrose's Law revisited: The relationship between mental institution beds, prison population and crime rate”. Nordic Journal of Psychiatry63 (1): 51–56. doi:10.1080/08039480802298697. hdl:10852/27918. PMID18985517.
Penrose, L. S.; Penrose, R. (February 1958). “Impossible Objects: A Special Type of Visual Illusion”. British Journal of Psychology49 (1): 31–33. doi:10.1111/j.2044-8295.1958.tb00634.x. PMID13536303.
Hartvig, P. L.; Kjelsberg, E. (2009). “Penrose's Law revisited: The relationship between mental institution beds, prison population and crime rate”. Nordic Journal of Psychiatry63 (1): 51–56. doi:10.1080/08039480802298697. hdl:10852/27918. PMID18985517.