Estimating trisection genus via gem theory

Gems are a particular type of edge-colored graphs, dual to colored triangulations, which represent compact PL-manifolds of arbitrary dimension, both in the closed and boundary case. In the present paper, gem theory is used to approach trisections of PL 4-manifolds, so as to prove that:
- the graph-defined invariant regular genus is an upper bound for the trisection genus of each closed 4-manifold;
- a trisection diagram can be directly obtained from any gem of a closed 4-manifold.
Moreover, suitable extensions of the above results are presented for compact 4-manifolds with connected boundary.