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　　pragma solidity>=0.5.0;
　　
　　import'uniswap/v2-core/contracts/interfaces/IUniswapV2Pair.sol';
　　
　　import"./SafeMath.sol";
　　
　　library UniswapV2Library{
　　
　　using SafeMath for uint;
　　
　　//returns sorted token addresses,used to handle return values from pairs sorted in this order
　　
　　function sortTokens(address tokenA,address tokenB)internal pure returns(address token0,address token1){
　　
　　require(tokenA!=tokenB,'UniswapV2Library:IDENTICAL_ADDRESSES');
　　
　　(token0,token1)=tokenA<tokenB?(tokenA,tokenB):(tokenB,tokenA);
　　
　　require(token0!=address(0),'UniswapV2Library:ZERO_ADDRESS');
　　
　　}
　　
　　//calculates the CREATE2 address for a pair without making any external calls
　　
　　// 在不进行任何外部调用的情况下计算一对的 CREATE2 地址
　　
　　function pairFor(address factory,address tokenA,address tokenB)internal pure returns(address pair){
　　
　　(address token0,address token1)=sortTokens(tokenA,tokenB);