Compatibility of the European Emissions Trading Scheme with interacting energy and climate policy instruments and measures : (executive summary) : creating scarcity through stringent targets and flexible control of the certificate supply / publisher: German Environment Agency, [German Emissions Trading Authority (DEHSt) at the German Environment Agency] ; E 2.3 draft by: Claudia Gibis, Jan Weiß, Christoph Kühleis ; contributers: Benjamin Lünenbürger, David Pfeiffer, Guido Knoche, Jürgen Landgrebe