code: def get_token_network_identifiers(
          chain_state: ChainState,
          payment_network_id: PaymentNetworkID,
  ) -> List[TokenNetworkID]:
      
      payment_network = chain_state.identifiers_to_paymentnetworks.get(payment_network_id)
  
      if payment_network is not None:
          return [
              token_network.address
              for token_network in payment_network.tokenidentifiers_to_tokennetworks.values()
          ]
  
      return list()
docs: Return the list of token networks registered with the given payment network.