These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.97 s (backtrack: 0/20).

[ebuild  N     ] sci-physics/hepmc-2.06.11-r1:2::gentoo  USE="-cm -doc -examples -gev -test" 4780 KiB

Total: 1 package (1 new), Size of downloads: 4780 KiB