How to add this repo using layman
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sudo layman -f -o https://git.backbone.ws/portage/overlay/blobs/raw/master/layman.xml -a backbone
Using Backbone's Profiles
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Default Desktop/Laptop Profile
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/etc/portage/make.profile/parent:
/var/portage/portage/profiles/default/linux/amd64/13.0
/var/portage/layman/backbone/profiles/desktop
Extreme Desktop/Laptop Profile
------------------------------
/etc/portage/make.profile/parent:
/var/portage/portage/profiles/default/linux/amd64/13.0
/var/portage/layman/backbone/profiles/extreme
Hardened Server Profile
------------------------------
/etc/portage/make.profile/parent:
/var/portage/portage/profiles/hardened/linux/amd64/no-multilib
/var/portage/layman/backbone/profiles/server
Remarks
=======
Also for Desktops/Laptops I recommend to use backbone-sources.