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Zentgraf, K., Heppe, H., Fleddermann, M. T. Julkaisussa German Journal of Exercise and Sport Research (2017) “...Heppe, H....”
Fleddermann, M.-T., Heppe, H., Eils, E., Zentgraf, K. Julkaisussa Just play it - "Innovative, international approaches to games" (2016) “...Heppe, H....”