code: def is_ens_domain(authority: str) -> bool:
      
      # check that authority ends with the tld '.eth'
      # check that there are either 2 or 3 subdomains in the authority
      # i.e. zeppelinos.eth or packages.zeppelinos.eth
      if authority[-4:] != ".eth" or len(authority.split(".")) not in [2, 3]:
          return False
      return True
docs: Return false if authority is not a valid ENS domain.