https://github.com/ethereum/solidity/blob/develop/Changelog.md#070-2020-07-28
Type checker: Disallow events with same name and parameter types in inheritance hierarchy.

Remove duplicate and conflict events

• IUniswapV2Pair
  • Approval
  • Transfer
• UniswapV2ERC20
  • Approval
  • Transfer
• UniswapV2Factory
  • PairCreated
• UniswapV2Pair
  • Mint
  • Burn
  • Swap
  • Sync

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https://github.com/ethereum/solidity/blob/develop/Changelog.md#060-2019-12-17
General: New reserved keywords: override, receive, and virtual.
https://docs.soliditylang.org/en/latest/contracts.html#function-overriding
The overriding function must then use the override keyword in the function header.

Add override keyword into child contract's functions and state variables if need

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1452_error, "Cannot override public state variable." Some functions inherit from bases both public function and public state variable two kinds. But second case couldn't be overridden.

Remove the conflict base contract's virtual functions.

• IUniswapV2Pair
  • name
  • symbol
  • decimals
  • totalSupply
  • balanceOf
  • allowance
  • approve
  • transfer
  • transferFrom
  • DOMAIN_SEPARATOR
  • PERMIT_TYPEHASH
  • nonces
  • permit

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Currently SOLL couldn't generate EWASM for constructor with parameters.

Remove parameter in constructor.

• UniswapV2Factory.sol

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• chainid -> chainid()
• Explicit type conversion
• Use type(Type).max replace Type(-1)