# burn ATokens
## Overview
* [x] cache
* [x] updateState
* [x] get user's AToken balance + amount to withdraw
* [x] validateWithdraw: confirm user has sufficient balance and asset isActive
* [x] updateInterestRates
* [x] collateral check
* [ ] burn ATokens
* [ ] Ensure existing loans are collateralized
## burn ATokens
* `burn` calls `_burnScaled`
Amount of tokens burnt is scaled against current liquidity index
* amount = 100
* liquidity index = 1.1
* `amountScaled` = 100 / 1.1 = 90
This is to account for interest accrued.
{% hint style="info" %}
If you are confused regarding `balanceIncrease` and `_userState` see: [mint](https://calnix.gitbook.io/aave-book/supply/transfer-and-mint#mint)
{% endhint %}
`_burnScaled` has an interesting approach, in that it looks to mint or burn the difference between unbooked interest accrued and the burn amount.
* unbooked interest accrued: interest accumulated since last update that has not been minted
**If `balanceIncrease > amount`**
* interest accrued since last update is larger than burn amount
* mint the difference to the user as aTokens
**If `balanceIncrease <= amount`**
* burn amount exceeds interest accrued
* burn the difference from the user
---
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## burn ATokens
* `burn` calls `_burnScaled`
