anchor.diff:    devtools = buildEnv {
       name = "devtools";
       paths = [
  -        git 
  +        git
           gitAndTools.tig
           ];
     };
  
positive.code: 
  rec {
  
    # source file so load bash environment with dependencies 
    policycompass-env = myEnvFun {
      name = "policycompass";
      buildInputs = with pkgs; [ policycompass ];
      extraCmds = 
          "export PYTHONHOME=${python34env}; export PATH=$PATH:${nodejs-env}/bin;"
      ;
    };
  
    # install dependencies 
    policycompass = buildEnv {
      name = "policycompass";
      paths = [
  
negative.code:         ];
    };
  
    python34env = buildEnv {
      name = "Python34Env";
      paths = [
          libxml2
  