# Summary

Thallo's two way carbon credit bridge is a suite of smart contracts that enables the issuance (bridging), retirement, and unbridging of Voluntary Carbon Credits (VCCs) in the form of fungible ERC20 tokens. Each token represents a unique project and vintage year combination. 

The ultimate goal of the bridge is to be a public, transparent ledger of all events related to the issuance and retirement of tokenized carbon credits conducted on Thallo's products. Thallo takes custody of the carbon credits backing the ERC20 tokens on-chain 1:1 on the underlying registry and then issues (mints) them as ERC20 tokens on the blockchain. All events conducted on the underlying registries will be reflected on-chain. The event log for each project and vintage is easily traceable through a single click function called **audit** which displays all issuance, retirement, and detokenization (uncustody) for that project and vintage. The **audit** function returns a trace log of all events that happened on the bridge, as well as information about the current token supply for that project and vintage.

When a company or individual user retires carbon credits through Thallo's platform, the retirement is reflected on the underlying registry and then the tokens are burned on-chain. The user is minted a Thallo Proof of Retirement NFT that commemorates this retirement and contains all relevant information about their retirement.

## Process Flows

<figure><img src="/files/Ydy9de7a165yjDNMZj0T" alt=""><figcaption><p>Smart Contract Process Flows</p></figcaption></figure>


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