We show that in the free group of rank 3, given an arbitrary number of automorphisms, the intersection of their fixed subgroups is equal to the fixed subgroup of some other single automorphism.
"Intersections of automorphism fixed subgroups in the free group of rank three." Algebr. Geom. Topol. 4 (1) 177 - 198, 2004. https://doi.org/10.2140/agt.2004.4.177