code: def open_recruitment(self, n=1):
          
          logger.info("Multi recruitment running for {} participants".format(n))
          recruitments = []
          messages = {}
          remaining = n
          for recruiter, count in self.recruiters(n):
              if not count:
                  break
              if recruiter.nickname in messages:
                  result = recruiter.recruit(count)
                  recruitments.extend(result)
              else:
                  result = recruiter.open_recruitment(count)
                  recruitments.extend(result["items"])
                  messages[recruiter.nickname] = result["message"]
  
              remaining -= count
              if remaining <= 0:
                  break
  
          logger.info(
              (
                  "Multi-recruited {} out of {} participants, " "using {} recruiters."
              ).format(n - remaining, n, len(messages))
          )
  
          return {"items": recruitments, "message": "\n".join(messages.values())}
docs: Return initial experiment URL list.