A repertory is an index of the homeopathic materia medica by symptom. A list of remedies is indicated for each symptom since a practitioner first needs to explore the remedies for a particular symptom rather than looking up the symptoms for a particular remedy. The "homeopathic repertory" lists after each symptom those remedies that are associated with it. Repertories are often very extensive and may include data extracted from multiple sources of materia medica. There is often lively debate among compilers of repertories and practitioners over the veracity of a particular inclusion.