anchor.diff: -{ stdenv
  -, lib
  +{ lib
  +, stdenv
   , buildPythonPackage
   , pythonOlder
   , fetchFromGitHub
  
positive.code:   ];
  
    disabledTestPaths = lib.optionals (!withContribRequires) [
      # requires external (unpackaged) libraries, so untested.
      "cirq/contrib/"
    ];
    disabledTests = [
      "test_metadata_search_path" # tries to import flynt, which isn't in Nixpkgs
      "test_benchmark_2q_xeb_fidelities" # fails due pandas MultiIndex. Maybe issue with pandas version in nix?
    ];
  
    meta = with lib; {
      broken = (stdenv.isLinux && stdenv.isAarch64);
      description = "Framework for creating, editing, and invoking Noisy Intermediate Scale Quantum (NISQ) circuits";
      homepage = "https://github.com/quantumlib/cirq";
      changelog = "https://github.com/quantumlib/Cirq/releases/tag/v${version}";
      license = licenses.asl20;
      maintainers = with maintainers; [ drewrisinger fab ];
    };
  }
  
negative.code: 
  buildPythonPackage rec {
    pname = "cirq-core";
    version = "1.0.0";
    format = "setuptools";
  
    disabled = pythonOlder "3.7";
  
    src = fetchFromGitHub {
      owner = "quantumlib";
      repo = "cirq";
      rev = "v${version}";
      hash = "sha256-KJ+z4zGrdGIXcGZzqHtWMf8aAzcn9CtltFawcHVldMQ=";
    };
  
    sourceRoot = "source/${pname}";
  