``` let sources = import ../nix/sources.nix; fetchGitHubArchive = { owner, repo, rev, sha256 }: builtins.fetchTarball { url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz"; inherit sha256; }; in import (fetchGitHubArchive { inherit (sources.emacs-overlay) owner repo rev sha256; }) ```