Paths sorted = topoSortPaths(*store, closure);

    writeStrings(sorted, to);

    writeStrings(closure, to);

    PathSet missing;
    std::set_difference(closure.begin(), closure.end(), present.begin(), present.end(),
        std::inserter(missing, missing.end()));

    if (present.size() == closure.size()) return;
    Paths sorted = topoSortPaths(*store, closure);
    Paths missing;
    for (auto i = sorted.rbegin(); i != sorted.rend(); ++i)
        if (present.find(*i) == present.end()) missing.push_back(*i);

    if (missing.empty()) return;

    writeInt(cmdImportPaths, to);
    exportPaths(*store, missing, false, to);
    to.flush();

    throw Error("NOT IMPL 1");

    if (readInt(from) != 1)
        throw Error("remote machine failed to import closure");