anchor.diff:    postInstall = ''
       for n in "$out/bin/"*; do wrapProgram "$n" --suffix MAUDE_LIB ':' "$out/share/maude"; done
       unzip ${fullMaude}
  -    install -D -m 444 full-maude3.maude $out/share/maude/full-maude.maude
  +    install -D -m 444 full-maude31.maude $out/share/maude/full-maude.maude
     '';
   
     # bison -dv surface.yy -o surface.c
  
positive.code:   inherit version;
  
    src = fetchurl {
      url = "http://maude.cs.illinois.edu/w/images/9/92/Maude-${version}.tar.gz";
      sha256 = "0vhn3lsck6ji9skrgm67hqrn3k4f6y442q73jbw65qqznm321k5a";
    };
  
    buildInputs = [
  
negative.code: 
  let
  
    version = "3.1";
  
    fullMaude = fetchurl {
      url = "http://maude.cs.illinois.edu/w/images/0/0a/Full-Maude-${version}.zip";
      sha256 = "8b13af02c6243116c2ef9592622ecaa06d05dbe1dd6b1e595551ff33855948f2";
    };
  
  in
  