It is a staple of mathematics that four into three won't go. It is a problem for Arsenal that four into four won't either: not without sacrifice, compromise and possible confusion anyway. Unai Emery can add the Arsenal attack to the issues he inherited.
Some would say they are the right kind of difficulties. Many clubs can only look on enviously at a quartet of Pierre-Emerick Aubameyang, Alexandre Lacazette, Mesut Ozil and Henrikh Mkhitaryan. They are arguably Arsenal's four best players and almost certainly the four best-paid.