diff --git a/src/FluxPair.sol b/src/FluxPair.sol
new file mode 100644
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--- /dev/null
+++ b/src/FluxPair.sol
@@ -0,0 +1,172 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.36;
+
+import {Erc20} from "./Erc20.sol";
+import {IErc20} from "./interfaces/IErc20.sol";
+import {IFluxCallee} from "./interfaces/IFluxCallee.sol";
+import {Math} from "./libraries/Math.sol";
+import {UQ112x112} from "./libraries/UQ112x112.sol";
+
+/// @title Constant-product pair holding reserves of two tokens and the LP token.
+contract FluxPair is Erc20 {
+    using UQ112x112 for uint224;
+
+    uint256 public constant minimumLiquidity = 10 ** 3;
+
+    address public factory;
+    address public token0;
+    address public token1;
+
+    uint112 private reserve0;
+    uint112 private reserve1;
+    uint32 private blockTimestampLast;
+
+    uint256 public price0CumulativeLast;
+    uint256 public price1CumulativeLast;
+
+    uint256 private unlocked = 1;
+
+    event Mint(address indexed sender, uint256 amount0, uint256 amount1);
+    event Burn(address indexed sender, uint256 amount0, uint256 amount1, address indexed to);
+    event Swap(
+        address indexed sender,
+        uint256 amount0In,
+        uint256 amount1In,
+        uint256 amount0Out,
+        uint256 amount1Out,
+        address indexed to
+    );
+    event Sync(uint112 reserve0, uint112 reserve1);
+
+    modifier lock() {
+        require(unlocked == 1, "Flux: LOCKED");
+        unlocked = 0;
+        _;
+        unlocked = 1;
+    }
+
+    constructor() Erc20("FluxSwap LP", "FLUX-LP") {
+        factory = msg.sender;
+    }
+
+    function initialize(address firstToken, address secondToken) external {
+        require(msg.sender == factory, "Flux: FORBIDDEN");
+        token0 = firstToken;
+        token1 = secondToken;
+    }
+
+    function getReserves()
+        public
+        view
+        returns (uint112 currentReserve0, uint112 currentReserve1, uint32 timestampLast)
+    {
+        currentReserve0 = reserve0;
+        currentReserve1 = reserve1;
+        timestampLast = blockTimestampLast;
+    }
+
+    function _safeTransfer(address token, address to, uint256 value) private {
+        (bool success, bytes memory returndata) =
+            token.call(abi.encodeWithSelector(IErc20.transfer.selector, to, value));
+        require(success && (returndata.length == 0 || abi.decode(returndata, (bool))), "Flux: TRANSFER_FAILED");
+    }
+
+    function _update(uint256 balance0, uint256 balance1, uint112 oldReserve0, uint112 oldReserve1) private {
+        require(balance0 <= type(uint112).max && balance1 <= type(uint112).max, "Flux: OVERFLOW");
+        uint32 blockTimestamp = uint32(block.timestamp % 2 ** 32);
+        unchecked {
+            uint32 timeElapsed = blockTimestamp - blockTimestampLast;
+            if (timeElapsed > 0 && oldReserve0 != 0 && oldReserve1 != 0) {
+                price0CumulativeLast += uint256(UQ112x112.encode(oldReserve1).uqdiv(oldReserve0)) * timeElapsed;
+                price1CumulativeLast += uint256(UQ112x112.encode(oldReserve0).uqdiv(oldReserve1)) * timeElapsed;
+            }
+        }
+        reserve0 = uint112(balance0);
+        reserve1 = uint112(balance1);
+        blockTimestampLast = blockTimestamp;
+        emit Sync(reserve0, reserve1);
+    }
+
+    function mint(address to) external lock returns (uint256 liquidity) {
+        (uint112 oldReserve0, uint112 oldReserve1,) = getReserves();
+        uint256 balance0 = IErc20(token0).balanceOf(address(this));
+        uint256 balance1 = IErc20(token1).balanceOf(address(this));
+        uint256 amount0 = balance0 - oldReserve0;
+        uint256 amount1 = balance1 - oldReserve1;
+
+        uint256 supply = totalSupply;
+        if (supply == 0) {
+            liquidity = Math.sqrt(amount0 * amount1) - minimumLiquidity;
+            _mint(address(0), minimumLiquidity);
+        } else {
+            liquidity = Math.min(amount0 * supply / oldReserve0, amount1 * supply / oldReserve1);
+        }
+        require(liquidity > 0, "Flux: INSUFFICIENT_LIQUIDITY_MINTED");
+        _mint(to, liquidity);
+
+        _update(balance0, balance1, oldReserve0, oldReserve1);
+        emit Mint(msg.sender, amount0, amount1);
+    }
+
+    function burn(address to) external lock returns (uint256 amount0, uint256 amount1) {
+        address firstToken = token0;
+        address secondToken = token1;
+        uint256 balance0 = IErc20(firstToken).balanceOf(address(this));
+        uint256 balance1 = IErc20(secondToken).balanceOf(address(this));
+        uint256 liquidity = balanceOf[address(this)];
+
+        uint256 supply = totalSupply;
+        amount0 = liquidity * balance0 / supply;
+        amount1 = liquidity * balance1 / supply;
+        require(amount0 > 0 && amount1 > 0, "Flux: INSUFFICIENT_LIQUIDITY_BURNED");
+        _burn(address(this), liquidity);
+        _safeTransfer(firstToken, to, amount0);
+        _safeTransfer(secondToken, to, amount1);
+        balance0 = IErc20(firstToken).balanceOf(address(this));
+        balance1 = IErc20(secondToken).balanceOf(address(this));
+
+        (uint112 oldReserve0, uint112 oldReserve1,) = getReserves();
+        _update(balance0, balance1, oldReserve0, oldReserve1);
+        emit Burn(msg.sender, amount0, amount1, to);
+    }
+
+    function swap(uint256 amount0Out, uint256 amount1Out, address to, bytes calldata data) external lock {
+        require(amount0Out > 0 || amount1Out > 0, "Flux: INSUFFICIENT_OUTPUT_AMOUNT");
+        (uint112 oldReserve0, uint112 oldReserve1,) = getReserves();
+        require(amount0Out < oldReserve0 && amount1Out < oldReserve1, "Flux: INSUFFICIENT_LIQUIDITY");
+
+        uint256 balance0;
+        uint256 balance1;
+        {
+            address firstToken = token0;
+            address secondToken = token1;
+            require(to != firstToken && to != secondToken, "Flux: INVALID_TO");
+            if (amount0Out > 0) _safeTransfer(firstToken, to, amount0Out);
+            if (amount1Out > 0) _safeTransfer(secondToken, to, amount1Out);
+            if (data.length > 0) IFluxCallee(to).fluxCall(msg.sender, amount0Out, amount1Out, data);
+            balance0 = IErc20(firstToken).balanceOf(address(this));
+            balance1 = IErc20(secondToken).balanceOf(address(this));
+        }
+        uint256 amount0In = balance0 > oldReserve0 - amount0Out ? balance0 - (oldReserve0 - amount0Out) : 0;
+        uint256 amount1In = balance1 > oldReserve1 - amount1Out ? balance1 - (oldReserve1 - amount1Out) : 0;
+        require(amount0In > 0 || amount1In > 0, "Flux: INSUFFICIENT_INPUT_AMOUNT");
+        {
+            uint256 balance0Adjusted = balance0 * 1000 - amount0In * 3;
+            uint256 balance1Adjusted = balance1 * 1000 - amount1In * 3;
+            require(balance0Adjusted * balance1Adjusted >= uint256(oldReserve0) * oldReserve1 * (1000 ** 2), "Flux: K");
+        }
+        _update(balance0, balance1, oldReserve0, oldReserve1);
+        emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
+    }
+
+    function skim(address to) external lock {
+        address firstToken = token0;
+        address secondToken = token1;
+        _safeTransfer(firstToken, to, IErc20(firstToken).balanceOf(address(this)) - reserve0);
+        _safeTransfer(secondToken, to, IErc20(secondToken).balanceOf(address(this)) - reserve1);
+    }
+
+    function sync() external lock {
+        _update(IErc20(token0).balanceOf(address(this)), IErc20(token1).balanceOf(address(this)), reserve0, reserve1);
+    }
+}