anchor.diff:  
     defaultVersion =  with versions;
       switch coq.version [
  +      { case = isEq "8.15"; out = "8.15.0+0.15.0"; }
         { case = isEq "8.14"; out = "8.14.0+0.14.0"; }
         { case = isEq "8.13"; out = "8.13.0+0.13.0"; }
         { case = isEq "8.12"; out = "8.12.0+0.12.1"; }
  
positive.code: 
  let
    release = {
      "8.14.0+0.14.0".sha256 = "sha256:1kh80yb791yl771qbqkvwhbhydfii23a7lql0jgifvllm2k8hd8d";
      "8.14+rc1+0.14.0".sha256 = "1w7d7anvcfx8vz51mnrf1jkw6rlpzjkjlr06avf58wlhymww7pja";
      "8.13.0+0.13.0".sha256 = "0k69907xn4k61w4mkhwf8kh8drw9pijk9ynijsppihw98j8w38fy";
      "8.12.0+0.12.1".sha256 = "048x3sgcq4h845hi6hm4j4dsfca8zfj70dm42w68n63qcm6xf9hn";
      "8.11.0+0.11.1".sha256 = "1phmh99yqv71vlwklqgfxiq2vj99zrzxmryj2j4qvg5vav3y3y6c";
  
negative.code:   let inherit (o) version; in {
    src = fetchzip {
      url =
          "https://github.com/ejgallego/coq-serapi/releases/download/${version}/coq-serapi-${
            if version == "8.11.0+0.11.1" then version
            else builtins.replaceStrings [ "+" ] [ "." ] version
  