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Determining the suitability of armed opposition elements as potential recipients of military assistance is complex and challenging. In Syria, such groups are numerous, rapidly evolving, and highly varied in ideology. Nevertheless, they do not pose an impenetrable mystery. Some are longstanding actors in the rebellion and currently hold or are contesting important areas of the country; a number of Free Syrian Army commanders are public personalities and can be contacted with relative ease. Vetting such actors is a critical prerequisite to providing military assistance, based on the recognition that not all armed elements should receive aid, and that some units are more worthy of aid than others. Moreover, vetting must not be done just in terms of outcomes on the battlefield -- equal...