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

Calculating dependencies ... done!
Dependency resolution took 1.04 s (backtrack: 0/20).

[ebuild  N     ] sci-mathematics/gmp-ecm-7.0.6-r1::gentoo  USE="custom-tune openmp" CPU_FLAGS_X86="sse2" 949 KiB
[ebuild  N     ] sci-mathematics/yafu-1.34.3-r2::gentoo  671 KiB

Total: 2 packages (2 new), Size of downloads: 1620 KiB