 It is hard to judge, though, as the choice can seldom be seen as an arbitrary one.Riley observes when Matthew has one or both halves of a Marcan dualism, it usually occurs where Matthew and Mark are following the same sequence; when Luke has one or both halves of a Marcan dualism, it "always" occurs where Luke and Mark are following the same sequence.This is expected under Marcan posteriority, assuming the Marcan account can more easily refer to Matthew from memory, but more difficult to explain under Marcan priority.