The hearings centered on Breivik's and the Norwegian government's appeals against an April 2016 Oslo court ruling that some of his human rights had been violated in prison.
The violations included "inhuman or degrading treatment or punishment" as defined by article three of the European Convention on Human Rights. Breivik's prolonged periods of isolation, lasting up to 23 hours, were also noted.
Breivik is serving a 21-year prison term for killing 77 people in two attacks targeting a summer camp and a Norwegian government building in 2011.
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