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

Calculating dependencies ...

!!! Problem resolving dependencies for =media-libs/vigra-1.12.1
 done!
Dependency resolution took 0.82 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=media-libs/vigra-1.12.1" has unmet requirements.
- media-libs/vigra-1.12.1::gentoo USE="fftw hdf5 jpeg png tiff zlib -doc -mpi -openexr -test" 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 )

  The above constraints are a subset of the following complete expression:
    exactly-one-of ( python_single_target_python3_12 python_single_target_python3_13 ) test? ( hdf5 fftw )