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Ellei muuten mainita, aineiston lisenssi on © This is an open access article published under Creative Commons Attribution-Noncommercial-NoDerivativeWorks 3.0 Unported licence. They may be copied, distributed and broadcast provided that the author and the e-journal that publishes them, eLearning Papers, are cited. Commercial use and derivative works are not permitted. The full licence can be consulted on http://creativecommons.org/ licenses/by-nc-nd/3.0/