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

Calculating dependencies ... done!
Dependency resolution took 1.49 s (backtrack: 0/20).

[ebuild     UD ] sys-kernel/linux-headers-3.18-r1::gentoo [6.19::gentoo] USE="-headers-only" 3692 KiB

Total: 1 package (1 downgrade), Size of downloads: 3692 KiB