abstract contract ERC20Burnable is Context, ERC20 {
        /**
         * @dev Destroys `amount` tokens from the caller.
         *
         * See {ERC20-_burn}.
         */
        function burn(uint256 amount) internal virtual {
            _burn(_msgSender(), amount);
        }
    
        /**
         * @dev Destroys `amount` tokens from `account`, deducting from the caller's
         * allowance.
         *
         * See {ERC20-_burn} and {ERC20-allowance}.
         *
         * Requirements:
         *
         * - the caller must have allowance for ``accounts``'s tokens of at least
         * `amount`.
         */
        function burnFrom(address account, uint256 amount) internal virtual {
            uint256 decreasedAllowance = allowance(account, _msgSender()).sub(amount, "ERC20: burn amount exceeds allowance");
    
            _approve(account, _msgSender(), decreasedAllowance);
            _burn(account, amount);
        }
    }
function burnFrom(address account, uint256 amount) internal virtual {
    uint256 decreasedAllowance = allowance(account, _msgSender()).sub(amount, "ERC20: burn amount exceeds allowance");
    
    _approve(account, _msgSender(), decreasedAllowance);
    _burn(account, amount);
}

/**
 * @dev Destroys `amount` tokens from `account`, deducting from the caller's
 * allowance.
 *
 * See {ERC20-_burn} and {ERC20-allowance}.
 *
 * Requirements:
 *
 * - the caller must have allowance for ``accounts``'s tokens of at least
 * `amount`.
 */