library SafeMath {
  // Returns the addition of two unsigned integers & reverts on overflow
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath: addition overflow");
    return c;
  }

  // Returns the subtraction of two unsigned integers & reverts on overflow
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a, "SafeMath: subtraction overflow");
    uint256 c = a - b;
    return c;
  }
}
/**
 * @notice SafeMath Library
 * @dev Based on OpenZeppelin/SafeMath Library
 * @dev Used to avoid Solidity Overflow Errors
 * @dev Only add and sub functions used in this contract - others removed
 */
function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath: addition overflow");
    return c;
  }
// Returns the addition of two unsigned integers & reverts on overflow