code: Task<String> createMailboxSummary(int id) {
      return Task.par(createExtendedSummary(id), fetchMailbox(id))
          .map("createMailboxSummary", (summary, mailbox) -> summary + " has " + mailbox.size() + " messages");
    }
docs: create mailbox summary for a person: "<first name> <last name> has <X> messages"