> For the complete documentation index, see [llms.txt](https://docs.zerolabs.green/zerolabs-tokenization-module/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zerolabs.green/zerolabs-tokenization-module/domain-definitions/bi-directional-link.md).

# Bi-directional link

In order to create an on-chain representation of the [Certificate](/zerolabs-tokenization-module/domain-definitions/certificate.md), we need to create a **bi-directional link** between the [redemption statement](/zerolabs-tokenization-module/domain-definitions/redemption-statement.md) and the on-chain Certificate/NFT.

### Link

A bi-directional link works in the following manner:

1. A [**Batch**](/zerolabs-tokenization-module/domain-definitions/batch.md) **ID has to be created**
   * A Batch ID is a randomly-generated **32 byte hex string**
   * Example: *0x56d5600d015ffabf32a5a572635d4370e235fc9953e87d9e731e8de7300f4fc1*
2. We use the Batch ID to create the following **redemption note** that needs to be attached to the redemption statement *(see below)*
3. **Attach the redemption statement** to the Batch by triggering an on-chain transaction. *See:* [*Setting the redemption statement*](https://app.gitbook.com/s/J1hmZlUO8raciusperMH/~/changes/MDjyuHE7FShHpYoEQgHB/domain-definitions/bi-directional-link/setting-the-redemption-statement)
4. **Issue** certificates from the redemption statement through the on-chain Batch. *See:* [*I*ssuance](https://app.gitbook.com/s/J1hmZlUO8raciusperMH/~/changes/P5GTpIhCn9Diil5OE1Fh/domain-definitions/bi-directional-link/issuance)

#### Redemption note example

> The certificates are redeemed for the purpose of tokenization and bridging to the Blockchain: Energy Web Chain with the Network ID 246. 
>
> The smart contract address is 0x2248a8E53c8cf533AEEf2369FfF9Dc8C036c8900 and the specific certificate batch ID is 795. 
>
> The bridging protocol used for tokenization is: ZeroLabs Renewable Energy Certificate Tokenization Protocol v1.0.0. 
>
> The certificates will be created as tokens of type ERC1888 - Topic: “1”.