anchor.diff:  { lib, mkCoqDerivation, coq, ssreflect, coq-ext-lib, simple-io, version ? null }:
   
   let recent = lib.versions.isGe "8.7" coq.coq-version; in
  -mkCoqDerivation {
  +(mkCoqDerivation {
     pname = "QuickChick";
     owner = "QuickChick";
     inherit version;
     defaultVersion = with lib; with versions; lib.switch [ coq.coq-version ssreflect.version ] [
  +      { cases = [ (isGe "8.13") pred.true  ]; out = "1.6.2"; }
         { cases = [ "8.13" pred.true  ]; out = "1.5.0"; }
         { cases = [ "8.12" pred.true  ]; out = "1.4.0"; }
         { cases = [ "8.11" pred.true  ]; out = "1.3.2"; }
  
positive.code:     description = "Randomized property-based testing plugin for Coq; a clone of Haskell QuickCheck";
      maintainers = with maintainers; [ jwiegley ];
    };
  }
  
negative.code:       { cases = [ "8.6"  pred.true  ];  out = "20171102"; }
        { cases = [ "8.5"  pred.true  ];  out = "20170512"; }
      ] null;
    release."1.6.2".sha256    = "0g5q9zw3xd4zndihq96nxkq4w3dh05418wzlwdk1nnn3b6vbx6z0";
    release."1.5.0".sha256    = "1lq8x86vd3vqqh2yq6hvyagpnhfq5wmk5pg2z0xq7b7dcw7hyfkw";
    release."1.4.0".sha256    = "068p48pm5yxjc3yv8qwzp25bp9kddvxj81l31mjkyx3sdrsw3kyc";
    release."1.3.2".sha256    = "0lciwaqv288dh2f13xk2x0lrn6zyrkqy6g4yy927wwzag2gklfrs";
  