> ## Documentation Index
> Fetch the complete documentation index at: https://tech.ramses.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Getting Started

<Note>
  Ramses V3 uses interfaces compatible with Uniswap V3, so you can use the `@uniswap/v3-periphery` and `@uniswap/v3-core` npm packages for interface definitions. The callback function names (`uniswapV3FlashCallback`, etc.) remain the same for compatibility.
</Note>

This guide builds a contract that calls `flash` on a Ramses V3 pool and arbitrages the price difference between pools with different fee tiers for the same token pair.

## Flash Transactions Overview

`flash` withdraws specified amounts of both `token0` and `token1` to a `recipient`. The withdrawn amount plus fees must be repaid by the end of the transaction. A `data` parameter allows passing arbitrary abi-encoded data to the callback.

```solidity theme={null}
    function flash(
        address recipient,
        uint256 amount0,
        uint256 amount1,
        bytes calldata data
    ) external override lock noDelegateCall {
```

## The Flash Callback

Inside `flash`, the pool calls back into `msg.sender`:

```solidity theme={null}
IUniswapV3FlashCallback(msg.sender).uniswapV3FlashCallback(fee0, fee1, data);
```

This is where you implement your custom logic. Three callbacks exist: `uniswapV3SwapCallback`, `uniswapV3MintCallback`, and `uniswapV3FlashCallback`.

## Contract Setup

Inherit `IUniswapV3FlashCallback` and `PeripheryPayments`. `PeripheryPayments` extends other contracts we need, including [LowGasSafeMath](../../reference/core/libraries/LowGasSafeMath).

```solidity theme={null}
pragma solidity =0.7.6;
pragma abicoder v2;

import '@uniswap/v3-core/contracts/interfaces/callback/IUniswapV3FlashCallback.sol';
import '@uniswap/v3-core/contracts/libraries/LowGasSafeMath.sol';

import '@uniswap/v3-periphery/contracts/base/PeripheryPayments.sol';
import '@uniswap/v3-periphery/contracts/base/PeripheryImmutableState.sol';
import '@uniswap/v3-periphery/contracts/libraries/PoolAddress.sol';
import '@uniswap/v3-periphery/contracts/libraries/CallbackValidation.sol';
import '@uniswap/v3-periphery/contracts/libraries/TransferHelper.sol';
import '@uniswap/v3-periphery/contracts/interfaces/ISwapRouter.sol';

contract PairFlash is IUniswapV3FlashCallback, PeripheryPayments {
    using LowGasSafeMath for uint256;
    using LowGasSafeMath for int256;

    ISwapRouter public immutable swapRouter;

    constructor(
        ISwapRouter _swapRouter,
        address _factory,
        address _WETH9
    ) PeripheryImmutableState(_factory, _WETH9) {
        swapRouter = _swapRouter;
    }
}
```