The `burn` function inside the UniswapV2Pair contract allows us to withdraw liquidity from a pair. When the `burn` function is called, it will send tokens to the address specified in the `to` input. The actual amount of each token that was withdrawn from the pool will be returned in the `amount0` and `amount1` outputs. We'll walk through the `burn` function line by line. The function first gets the balance of token0 and token1: ```javascript address token0 = IERC20(token).balance(address(this)); ``` ```javascript address token1 = IERC20(token).balance(address(this)); ``` Next, it calls an internal function `mintFee`: ```javascript bool feeOn = mintFee(reserve0, reserve1); ``` We've covered `mintFee` in a previous lesson. The `burn` function calculates the amount of token0 and token1 to send to the `to` address using this equation: ```javascript amount0 = liquidity * mul(balance0 / totalSupply, reserve0); ``` ```javascript amount1 = liquidity * mul(balance1 / totalSupply, reserve1); ``` This formula calculates the proportional share of the total reserves for each token based on the liquidity being withdrawn. Next, the `burn` function checks that the amount of each token to send is greater than zero: ```javascript require(amount0 > 0 && amount1 > 0, 'UniswapV2: INSUFFICIENT_LIQUIDITY_BURNED'); ``` After that, the function burns the liquidity shares that we've withdrawn from the pool. ```javascript burn(address(this), liquidity); ``` Finally, the `burn` function updates the balance of each token in the pool to reflect the liquidity withdrawal. ```javascript balance0 = IERC20(token0).balanceOf(address(this)); ``` ```javascript balance1 = IERC20(token1).balanceOf(address(this)); ``` This ensures that the balances are up-to-date. The last step is to update the internal state of the pool: ```javascript update(balance0, balance1, reserve0, reserve1); ``` This ensures that the `reserve0` and `reserve1` values are updated to reflect the changes in the pool's balances.