Original sentence: Bulgarian origin, a view that is common among the Bulgarian historians who reckon that all native sources use predominantly the terms Bulgaria, Bulgarians and Bulgarian, that tsar Kaloyan claimed provenance from the rulers of the First Bulgarian Empire and that it's just a matter of terminology and for certain period by "Vlach" the medieval sources meant "Bulgarian".Cuman' origin, as some of the names in the dynasty, including Asen and Belgun (nickname of Ivan Asen I) are derived from Cuman language
Edited sentence: Bulgarian' origin, a view that is common among the Bulgarian historians who reckon that all native sources use predominantly the terms Bulgaria, Bulgarians and Bulgarian, that tsar Kaloyan claimed provenance from the rulers of the First Bulgarian Empire and that it's just a matter of terminology and for certain period by "Vlach" the medieval sources meant "Bulgarian".Cuman origin, as some of the names in the dynasty, including Asen and Belgun (nickname of Ivan Asen I) are derived from Cuman language