UNI vs RING

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/**
// SPDX-License-Identifier: GPL-2.0-or-later
*Submitted for verification at Etherscan.io on 2020-09-16
pragma solidity =0.7.6;
*/

/**
*Submitted for verification at Etherscan.io on 2020-09-15
*/

pragma solidity ^0.5.16;
pragma experimental ABIEncoderV2;
pragma experimental ABIEncoderV2;


// From https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/Math.sol
// Forked from Uniswap's UNI
// Subject to the MIT license.
// Reference: https://etherscan.io/address/0x1f9840a85d5af5bf1d1762f925bdaddc4201f984#code

/**
* @dev Wrappers over Solidity's arithmetic operations with added overflow
* checks.
*
* Arithmetic operations in Solidity wrap on overflow. This can easily result
* in bugs, because programmers usually assume that an overflow raises an
* error, which is the standard behavior in high level programming languages.
* `SafeMath` restores this intuition by reverting the transaction when an
* operation overflows.
*
* Using this library instead of the unchecked operations eliminates an entire
* class of bugs, so it's recommended to use it always.
*/
library SafeMath {
/**
* @dev Returns the addition of two unsigned integers, reverting on overflow.
*
* Counterpart to Solidity's `+` operator.
*
* Requirements:
* - Addition cannot overflow.
*/
function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a, "SafeMath: addition overflow");

return c;
}

/**
* @dev Returns the addition of two unsigned integers, reverting with custom message on overflow.
*
* Counterpart to Solidity's `+` operator.
*
* Requirements:
* - Addition cannot overflow.
*/
function add(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a, errorMessage);

return c;
}

/**
* @dev Returns the subtraction of two unsigned integers, reverting on underflow (when the result is negative).
*
* Counterpart to Solidity's `-` operator.
*
* Requirements:
* - Subtraction cannot underflow.
*/
function sub(uint256 a, uint256 b) internal pure returns (uint256) {
return sub(a, b, "SafeMath: subtraction underflow");
}

/**
* @dev Returns the subtraction of two unsigned integers, reverting with custom message on underflow (when the result is negative).
*
* Counterpart to Solidity's `-` operator.
*
* Requirements:
* - Subtraction cannot underflow.
*/
function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
require(b <= a, errorMessage);
uint256 c = a - b;

return c;
}

/**
* @dev Returns the multiplication of two unsigned integers, reverting on overflow.
*
* Counterpart to Solidity's `*` operator.
*
* Requirements:
* - Multiplication cannot overflow.
*/
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
// benefit is lost if 'b' is also tested.
// See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
if (a == 0) {
return 0;
}