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

Calculating dependencies ...

!!! Problem resolving dependencies for =app-doc/cppman-0.5.9
 done!
Dependency resolution took 0.85 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=app-doc/cppman-0.5.9" has unmet requirements.
- app-doc/cppman-0.5.9::gentoo USE="" PYTHON_SINGLE_TARGET="-python3_12 -python3_13"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( python_single_target_python3_12 python_single_target_python3_13 )