 Some theories deny literary priority to any one of the Synoptic Gospels, asserting that, whatever their chronological order of composition, none of them draws from any of the others.The multi-source theory has each synoptic gospel combining a distinct mix of earlier documents, while the independence theory denies any documentary relationship and regards each gospel as an original composition utilizing oral sources only.Some variations on Marcan priority propose an additional revision of Mark—a "Proto-Mark" ("Ur-Mark") if earlier than the canonical Gospel, or a "Deutero-Mark" if later—serving as a source for Matthew and/or Luke.