anchor.diff:  { stdenv, fetchgit, perl, cdrkit, syslinux, xz, openssl }:
   
   let
  -  date = "20160831";
  -  rev = "827dd1bfee67daa683935ce65316f7e0f057fe1c";
  +  date = "20170922";
  +  rev = "74d90b33f8490adcee2026ece18d8411d93b6a39";
   in
   
   stdenv.mkDerivation {
  
positive.code:   installPhase = ''
      mkdir -p $out
      cp bin/ipxe.dsk bin/ipxe.usb bin/ipxe.iso bin/ipxe.lkrn bin/undionly.kpxe $out
    '';
  
    meta = with stdenv.lib;
  
negative.code: 
    src = fetchgit {
      url = git://git.ipxe.org/ipxe.git;
      sha256 = "12ijrq451fj2x3i7c7xjlxig5mwbhmgzqjvmfl2sza953vfbk4vw";
      inherit rev;
    };
  
  