anchor.diff:      libgcrypt
       libgpg-error
       libksba
  -    libusb
  -    npth
  +    libusb'
  +    pth'
       openldap
       readline
       sqlite
       zlib
  +  ] ++ optionals (versionOlder version "2.1") [
  +    curl
     ];
   
     postPatch = ''
  
positive.code: let
    inherit (stdenv)
      targetSystem;
    inherit (stdenv.lib)
      elem
      optional
      platforms;
  in
  
  let
    sources = import ./sources.nix;
  
    tarballUrls = version: [
  
negative.code:   ];
  
    version = sources.${channel}.version;
  
    libusb' =
      if versionAtLeast channel "2.1" then
        libusb
      else
        libusb-compat;
  
    pth' =
      if versionAtLeast channel "2.1" then
        npth
      else
        pth;
  in
  
  stdenv.mkDerivation rec {
  