anchor.diff:          services = {
   	  xserver = {
   	    enable = true;
  -            driSupport = true;
  +
  +            displayManager = {
  +	      slim = {
  +	        enable = false;
  +	      };
  +              kdm = {
  +	        enable = true;
  +		extraConfig =
  +                  ''
  +                    [X-:0-Core]
  +                    AutoLoginEnable=true
  +                    AutoLoginUser=alice
  +                    AutoLoginPass=foobar
  +                  '';
  +	      };
  +	    };
  +	    desktopManager = {
  +	      default = "kde4";
  +	      kde4 = {
  +	        enable = true;
  +	      };
  +	    };            
   	  };
   	};
  -	  
  +	
  +	users = {
  +	  extraUsers = pkgs.lib.singleton { 
  +	      name = "alice";
  +              description = "Alice Foobar";
  +              home = "/home/alice";
  +              createHome = true;
  +              useDefaultShell = true;
  +              password = "foobar";
  +          };
  +        };
  + 
           environment = {
   	  extraPackages = [
  -	    pkgs.firefox
  -	    pkgs.icewm
  +	    pkgs.firefoxWrapper
   	    pkgs.scrot
   	  ];
   	};
  
positive.code:     
            postgresql = {
              enable = true;
        
              authentication = ''
                # Generated file; do not edit!
                local all all              trust
                host  all all 127.0.0.1/32 trust
  	      host  all all ::1/128      trust
              '';
            };
          };  
  
negative.code:       {config, pkgs, ...}:
        {
          services = {
  	  portmap = {
  	    enable = true;
  	  };
  
            nfsKernel = {
              enable = true;
            };	  
    
            httpd = {
              enable = true;
  