20 uniswap中首次添加流动性不减去最小流动性MINIMUM_LIQUIDITY那个1000会有什么问题，什么是LP操纵？

if (_totalSupply == 0) {
    liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
   _mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
}