SBL/AARdvent Calendar: Day 2

Two questions for every New Testament scholar: 
1) How confident are you that Mark was the first Gospel?
2) How confident are you that the Synoptic Problem is solved?

2018 year saw the publication of Gospel Interpretation and the Q-Hypothesis edited by Mogens Müller and Heike Omerzu (LNTS, Bloomsbury). This represents selected output from a conference held in Roskilde, Denmark in 2015 - at which a high proportion of the best, currently active, Synoptic Problem specialist were present. The volume is striking in two respects. First, every contributor is confident that Mark is the first of the three Synoptic Gospels. Second, it is remarkable how often contributors state something along the lines of: 'the Synoptic Problem is not yet solved'.

This state of affairs is worth reflecting upon.

If we are confident that Mark was first, then this leaves three possible (simple) solutions:
1) Matthew used Luke
2) Luke used Matthew
3) Matthew and Luke independently used Q

If, after decades of sustained enquiry, we continue to suspect that options 2) and 3) don't fully solve the Problem, then it follows that option 1) might, after all, be correct. 

So, if you are very confident that Mark is the first Gospel, while also suspecting that the Synoptic Problem has not yet been solved (by the mainstream hypotheses), then may I encourage you to consider option 1): Matthew used Luke?