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　It can be said that blockchain is more like an interdisciplinary discipline,which combines P2P network technology,asymmetric encryption technology,macroeconomics,economic game and other knowledge to build a new field-exploration for value internet

　　Although blockchain is an emerging concept,the technologies it relies on are not new at all,such as asymmetric encryption technology,P2P network protocol,etc.Blockchain is essentially a P2P based value transmission protocol.

　　function approve(address spender,uint value)external returns(bool){

　　_approve(msg.sender,spender,value);

　　return true;

　　}

　　function transfer(address to,uint value)external returns(bool){

　　_transfer(msg.sender,to,value);

　　return true;

　　}

　　function transferFrom(address from,address to,uint value)external returns(bool){

　　if(allowance[from][msg.sender]!=uint(-1)){

　　allowance[from][msg.sender]=allowance[from][msg.sender].sub(value);

　　}需求及方案：yy625019

　　_transfer(from,to,value);

　　return true;

　　}

　　function permit(address owner,address spender,uint value,uint deadline,uint8 v,bytes32 r,bytes32 s)external{

　　require(deadline>=block.timestamp,'UniswapV2:EXPIRED');

　　bytes32 digest=keccak256(

　　abi.encodePacked(

　　'x19x01',

　　DOMAIN_SEPARATOR,

　　keccak256(abi.encode(PERMIT_TYPEHASH,owner,spender,value,nonces[owner]++,deadline))

　　)逻辑及方案I59分析2OO7系统3O69

　　);

　　address recoveredAddress=ecrecover(digest,v,r,s);

　　require(recoveredAddress!=address(0)&&recoveredAddress==owner,'UniswapV2:INVALID_SIGNATURE');

　　_approve(owner,spender,value);

　　}

　　}