Another important phenomenon is that Mark's wording is usually fuller than either Matthew's or Luke's. This fact has been used to argue against the notion that Mark is an abridgement, but others see it as indicating that Mark is secondary. This area of the Synoptic Problem has been riddled with reversible and inconclusive arguments. Basically, such redactional arguments can provide equally compelling reasons for an addition or for a deletion. This is a brief overview of the solutions to the Synoptic Problem, starting from the most widely held, near-consensus theory and its major challenger.
Many problems remain.
The International Q Project is currently engaged to this task. Holtzmann's 1863 theory posited an Ur-Marcus in the place of our Mark, with our Mark being a later revision. Some scholars occasionally propose an unattested revision of Mark, a deutero-Mark, being the base of what Matthew and Luke used. While unique sources, such as M, L, or Semitic first editions, are interesting for form-critical purposes, they are quite peripheral to the Synoptic Problem as to how the canonical gospels are interrelated. The Griesbach hypothesis holds that Matthew was written first, and Luke used it in preparing his gospel.