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What a pity! But here we go: In your own Karma Overview click the Button "Configuration". It is located in the upper right corner of the screen. Simply deselect your participation in the pop-up and you won't be listed anymore. If you want to join again, you won't have to start from the scratch. Just select the participation again and you will start, where you left (except the configuration is set to loose lose Karma over the time, if you are not active.).
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