***可以运行代码。尽管*初的***用于简单的程序，主要是令牌事务，但是技术的进步使它能够执行更复杂的事务并识别出**良好的编程语言。
因为这些程序在***系统-176搭建-0206+可电可微-5616上运行，所以它们的特性不同于其他软件。
首先，程序本身被记录在块链上，
因此具有***的**性和非审计性；模式**威：ww, 其次，程序可以控制***资产，例如可以存储和传输加密货币；第三，程序由***执行。
Blockchain is a new application model for computer technology such as distributed data storage,peer-to-peer transmission,consensus mechanism,and encryption algorithms.
Narrowly speaking,blockchain is a chain like data structure that combines data blocks in chronological order and ensures that they are tamper proof and unforgeable in a cryptologically secure distributed ledger.
Broadly speaking,blockchain technology is a new distributed infrastructure and computing method that utilizes blockchain data structures to validate and store data,distributed node consensus algorithms to generate and update data,cryptography to ensure data transmission and access security,and smart contracts composed of automated script code to program and operate data
什么是 DAPP？DAPP 是 Decentralized Application 的缩写，中文叫分布式应用 / 去中心化应用。通常来说，不同的 DAPP 会采用不同的底层技术**平台和共识机制，或者自行发布代币。
//returns sorted token addresses,used to handle return values from pairs sorted in this order
// 两个地址排序
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');
