> For the complete documentation index, see [llms.txt](https://dev.bondprotocol.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dev.bondprotocol.finance/smart-contracts/bond-system/teller/fixed-expiry-teller.md).

# Fixed-Expiry Teller

The [Fixed Expiry Teller](https://github.com/Bond-Protocol/bond-contracts/blob/master/src/BondFixedExpiryTeller.sol) is an implementation of the [Base Teller](/smart-contracts/bond-system/teller/base-teller.md) contract specific to handling user bond transactions and tokenizing bond markets where all purchases vest at the same timestamp as ERC20 tokens. It implements the functions required by the [Fixed-Expiry Teller Interface](/smart-contracts/bond-system/teller/teller-interfaces.md#fixed-expiry-teller-interface). 

Specifically, it implements the `_handlePayout` function to mint ERC20 tokens to the user to represent their bond position during a purchase. 

Additionally, it implements the `deploy` (deploys new ERC20 token contract if one does not exist for a combination of underlying token and the maturity date), `create` (allows anyone to mint Bond Tokens for a combination of an underlying token and maturity date by paying a fee to the protocol), and `redeem` (redeems ERC20 Bond Tokens that have vested for the underlying token). 

By design, the tokenization of the Teller is not permissioned. This allows other participants to use the same ERC20 Bond Tokens that Bond Protocol is issuing to create a standard in the market and drive additional liquidity.

## Methods

This section only includes methods not inherited from [Base Teller](/smart-contracts/bond-system/teller/base-teller.md).

### bondTokenImplementation

```solidity
function bondTokenImplementation() external view returns (contract ERC20BondToken)
```

ERC20BondToken reference implementation (deployed on creation to clone from)

#### Returns

| Name      | Type                    | Description                                                                          |
| --------- | ----------------------- | ------------------------------------------------------------------------------------ |
| reference | contract ERC20BondToken | reference address that each ERC20 bond token proxies to (using a Clone architecture) |

### bondTokens

```solidity
function bondTokens(contract ERC20, uint48) external view returns (contract ERC20BondToken)
```

ERC20 bond tokens (unique to a underlying and expiry)

#### Parameters

| Name       | Type           | Description                           |
| ---------- | -------------- | ------------------------------------- |
| underlying | contract ERC20 | Address of the underlying ERC20 token |
| expiry     | uint48         | Expiry of the bond token              |

#### Returns

| Name      | Type                    | Description                     |
| --------- | ----------------------- | ------------------------------- |
| bondToken | contract ERC20BondToken | Address of the ERC20 bond token |

### create

```solidity
function create(contract ERC20 underlying_, uint48 expiry_, uint256 amount_) external nonpayable returns (contract ERC20BondToken, uint256)
```

Deposit an ERC20 token and mint a future-dated ERC20 bond token

#### Parameters

| Name         | Type           | Description                                                                |
| ------------ | -------------- | -------------------------------------------------------------------------- |
| underlying\_ | contract ERC20 | ERC20 token redeemable when the bond token vests                           |
| expiry\_     | uint48         | Timestamp at which the bond token can be redeemed for the underlying token |
| amount\_     | uint256        | Amount of underlying tokens to deposit                                     |

#### Returns

| Name      | Type                    | Description                              |
| --------- | ----------------------- | ---------------------------------------- |
| bondToken | contract ERC20BondToken | Address of the ERC20 bond token received |
| amountOut | uint256                 | Amount of the ERC20 bond token received  |

### deploy

```solidity
function deploy(contract ERC20 underlying_, uint48 expiry_) external nonpayable returns (contract ERC20BondToken)
```

Deploy a new ERC20 bond token for an (underlying, expiry) pair and return its address

*ERC20 used for fixed-expiryIf a bond token exists for the (underlying, expiry) pair, it returns that address*

#### Parameters

| Name         | Type           | Description                                                                |
| ------------ | -------------- | -------------------------------------------------------------------------- |
| underlying\_ | contract ERC20 | ERC20 token redeemable when the bond token vests                           |
| expiry\_     | uint48         | Timestamp at which the bond token can be redeemed for the underlying token |

#### Returns

| Name      | Type                    | Description                                   |
| --------- | ----------------------- | --------------------------------------------- |
| bondToken | contract ERC20BondToken | Address of the ERC20 bond token being created |

### getBondTokenForMarket

```solidity
function getBondTokenForMarket(uint256 id_) external view returns (contract ERC20BondToken)
```

Get the OlympusERC20BondToken contract corresponding to a market

#### Parameters

| Name | Type    | Description      |
| ---- | ------- | ---------------- |
| id\_ | uint256 | ID of the market |

#### Returns

| Name      | Type                    | Description                     |
| --------- | ----------------------- | ------------------------------- |
| bondToken | contract ERC20BondToken | ERC20BondToken contract address |

### redeem

```solidity
function redeem(contract ERC20BondToken token_, uint256 amount_) external nonpayable
```

Redeem a fixed-expiry bond token for the underlying token (bond token must have matured)

#### Parameters

| Name     | Type                    | Description      |
| -------- | ----------------------- | ---------------- |
| token\_  | contract ERC20BondToken | Token to redeem  |
| amount\_ | uint256                 | Amount to redeem |

## Events

### ERC20BondTokenCreated

```solidity
event ERC20BondTokenCreated(contract ERC20BondToken bondToken, contract ERC20 indexed underlying, uint48 indexed expiry)
```

#### Parameters

| Name                 | Type                    | Description                                                            |
| -------------------- | ----------------------- | ---------------------------------------------------------------------- |
| bondToken            | contract ERC20BondToken | Address of the bond token                                              |
| underlying `indexed` | contract ERC20          | Address of the underlying ERC20 token                                  |
| expiry `indexed`     | uint48                  | Timestamp when the bond token can be redeemed for the underlying token |