APNsL13 /etc/portage/package.use # cat apfel 
    sci-physics/apfel python_single_target_python3_10 -python_single_target_python3_11
    APNsL13 /etc/portage/package.use # emerge --verbose y --usepkg-exclude sci-physics/apfel --deep --backtrack 300 --autounmask=y --autounmask-write --autounmask-continue --autounmask-use=y --autounmask-backtrack=y =sci-physics/apfel-3.1.1

     * IMPORTANT: 9 config files in '/etc/portage' need updating.
     * See the CONFIGURATION FILES and CONFIGURATION FILES UPDATE TOOLS
     * sections of the emerge man page to learn how to update config files.

    Local copy of remote index is up-to-date and will be used.

    Local copy of remote index is up-to-date and will be used.

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

    Calculating dependencies... done!
    Dependency resolution took 2.22 s (backtrack: 0/300).
    

    The following USE changes are necessary to proceed:
     (see "package.use" in the portage(5) man page for more details)
    # required by sci-physics/apfel-3.1.1::hep-forge
    # required by =sci-physics/apfel-3.1.1 (argument)
    >=sci-physics/lhapdf-6.5.4 python_single_target_python3_10

    Autounmask changes successfully written.

     * IMPORTANT: 10 config files in '/etc/portage' need updating.
     * See the CONFIGURATION FILES and CONFIGURATION FILES UPDATE TOOLS
     * sections of the emerge man page to learn how to update config files.

    !!! The ebuild selected to satisfy "sci-physics/lhapdf[python(+),python_single_target_python3_10(-)?,python_single_target_python3_11(-)?]" has unmet requirements.
    - sci-physics/lhapdf-6.5.4::hep-forge USE="-doc -examples" ABI_X86="(64)" PYTHON_SINGLE_TARGET="python3_11 -python3_10"

      The following REQUIRED_USE flag constraints are unsatisfied:
        exactly-one-of ( python_single_target_python3_10 python_single_target_python3_11 )

    (dependency required by "sci-physics/apfel-3.1.1::hep-forge" [ebuild])
    (dependency required by "=sci-physics/apfel-3.1.1" [argument])