## Solution: Uniswap V3 Swap rEth to wEth Let's delve into the solution for swapping our rEth back into wEth using Uniswap V3. We'll be using the internal function `swap`, which handles the specifics of interacting with Uniswap V3. Our task is to pass the correct parameters to this internal function. These parameters include `tokenIn`, `tokenOut`, `fee`, `amountIn`, `amountOutMin`, and the `receiver`. In the process of swapping our rEth back to wEth, we first need to transfer rEth from the message sender into the contract. Then, we approve the Uniswap V3 router to use that rEth from this contract. ```solidity reth.transferFrom(msg.sender, address(this), rEthAmount); ``` Next, we approve the Uniswap V3 router. ```solidity reth.approve(address(router), rEthAmount); ``` Following this, we call the internal function `swap`: ```solidity swap( ); ``` We define `tokenIn` as rEth and `tokenOut` as wEth: ```solidity swap( RETH, WETH, ); ``` The pool fee, which identifies the pool, is a constant imported at the top of the file. Let’s copy that, go back down, and paste it. ```solidity swap( RETH, WETH, UNISWAP_V3_POOL_FEE_RETH_WETH, ); ``` Next, we include the amount in: ```solidity swap( RETH, WETH, UNISWAP_V3_POOL_FEE_RETH_WETH, rEthAmountIn, ); ``` After this, we specify the amount out min: ```solidity swap( RETH, WETH, UNISWAP_V3_POOL_FEE_RETH_WETH, rEthAmountIn, wEthAmountOutMin, ); ``` Finally, we define the receiver of wEth: ```solidity swap( RETH, WETH, UNISWAP_V3_POOL_FEE_RETH_WETH, rEthAmountIn, wEthAmountOutMin, address(this) ); ``` With the code complete, we can now execute the test. The test command is as follows: ```bash forge test --fork-url $FORK_URL --match-path test/exercise-swap-uniswap-v3.sol --match-test test_swapRethToWeth -vvv ``` In this command, the test file is `exercise-swap-uniswap-v3.sol`, and the function we're calling is `test_swapRethToWeth`. The execution gives us back approximately 1.120 wEth.