anchor.diff:    inherit version;
   
     src = fetchurl {
  -    url = "http://maude.cs.illinois.edu/w/images/9/92/Maude-${version}.tar.gz";
  -    sha256 = "0vhn3lsck6ji9skrgm67hqrn3k4f6y442q73jbw65qqznm321k5a";
  +    url = "http://maude.cs.illinois.edu/w/images/d/d3/Maude-${version}.tar.gz";
  +    sha256 = "b112d7843f65217e3b5a9d40461698ef8dab7cbbe830af21216dfb924dc88a2f";
     };
   
     buildInputs = [
  
positive.code: 
  let
  
    version = "3.0";
  
    fullMaude = fetchurl {
      url = "http://maude.cs.illinois.edu/w/images/0/04/Full-Maude-${version}.zip";
      sha256 = "0gf36wlkkl343vlxgryqdhxmgyn8z0cc2zayccd7ac3inmj1iayw";
    };
  
  in
  
negative.code:   postInstall = ''
      for n in "$out/bin/"*; do wrapProgram "$n" --suffix MAUDE_LIB ':' "$out/share/maude"; done
      unzip ${fullMaude}
      install -D -m 444 full-maude31.maude $out/share/maude/full-maude.maude
    '';
  
    # bison -dv surface.yy -o surface.c
  