Editors. "Protestant princes ordered to conform by 15th April 1531". The Literary Encyclopedia. First published 01 November 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=14451, accessed 23 May 2013.]
The Diet of Augsburg rules that the Protestant princes of Germany must conform, by disowning their heretical attachment to Martin Luther and his doctrines, by 15th April 1531.