anchor.diff:      /*
       "rhel-6" = {
         image = import <nix/fetchurl.nix> {
  -        url = https://app.vagrantup.com/generic/boxes/rhel6/versions/4.1.12/providers/libvirt.box;
  +        url = "https://app.vagrantup.com/generic/boxes/rhel6/versions/4.1.12/providers/libvirt.box";
           hash = "sha256-QwzbvRoRRGqUCQptM7X/InRWFSP2sqwRt2HaaO6zBGM=";
         };
         rootDisk = "box.img";
  
positive.code: 
      "rhel-9" = {
        image = import <nix/fetchurl.nix> {
          url = https://app.vagrantup.com/generic/boxes/rhel9/versions/4.1.12/providers/libvirt.box;
          hash = "sha256-vL/FbB3kK1rcSaR627nWmScYGKGk4seSmAdq6N5diMg=";
        };
        rootDisk = "box.img";
  
negative.code: 
      "ubuntu-16-04" = {
        image = import <nix/fetchurl.nix> {
          url = "https://app.vagrantup.com/generic/boxes/ubuntu1604/versions/4.1.12/providers/libvirt.box";
          hash = "sha256-lO4oYQR2tCh5auxAYe6bPOgEqOgv3Y3GC1QM1tEEEU8=";
        };
        rootDisk = "box.img";
  