anchor.diff:    };
   
     prefixKey = "-prefix ";
  -  configureFlags = ["-no-tk"] ++ optionals useX11 [ "-x11lib" x11 ];
  +  configureFlags = ["-no-tk"] ++ optionals useX11 [ "-x11lib" x11lib
  +                                                    "-x11include" x11inc ];
  +
     buildFlags = "world" + optionalString useNativeCompilers " bootstrap world.opt";
  -  buildInputs = [ncurses] ++ optionals useX11 [ x11 ];
  +  buildInputs = [ncurses] ++ optionals useX11 [ libX11 xproto ];
     installTargets = "install" + optionalString useNativeCompilers " installopt";
     preConfigure = ''
       CAT=$(type -tp cat)
  
positive.code: { stdenv, fetchurl, ncurses, x11 }:
  
  let
     useX11 = !stdenv.isArm && !stdenv.isMips;
  
negative.code: 
  stdenv.mkDerivation rec {
  
    x11env = buildEnv { name = "x11env"; paths = [libX11 xproto]; };
    x11lib = x11env + "/lib";
    x11inc = x11env + "/include";
  
    name = "ocaml-4.01.0";
  
    src = fetchurl {
  