library Address {
 /**
 * @dev Returns true if `account` is a contract.
 *
 * [IMPORTANT]
 * ====
 * It is unsafe to assume that an address for which this function returns
 * false is an externally-owned account (EOA) and not a contract.
 *
 * Among others, `isContract` will return false for the following
 * types of addresses:
 *
 * - an externally-owned account
 * - a contract in construction
 * - an address where a contract will be created
 * - an address where a contract lived, but was destroyed
 * ====
 */
 function isContract(address account) internal view returns (bool) {
 // This method relies on extcodesize, which returns 0 for contracts in
 // construction, since the code is only stored at the end of the
 // constructor execution.

 uint256 size;
 assembly {
 size := extcodesize(account)
 }
 return size > 0;
 }

 /**
 * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
 * `recipient`, forwarding all available gas and reverting on errors.
 *
 * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
 * of certain opcodes, possibly making contracts go over the 2300 gas limit
 * imposed by `transfer`, making them unable to receive funds via
 * `transfer`. {sendValue} removes this limitation.
 *
 * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
 *
 * IMPORTANT: because control is transferred to `recipient`, care must be
 * taken to not create reentrancy vulnerabilities. Consider using
 * {ReentrancyGuard} or the
 * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
 */
 function sendValue(address payable recipient, uint256 amount) internal {
 require(address(this).balance >= amount, "Address: insufficient balance");

 (bool success, ) = recipient.call{value: amount}("");
 require(success, "Address: unable to send value, recipient may have reverted");
 }

 /**
 * @dev Performs a Solidity function call using a low level `call`. A
 * plain `call` is an unsafe replacement for a function call: use this
 * function instead.
 *
 * If `target` reverts with a revert reason, it is bubbled up by this
 * function (like regular Solidity function calls).
 *
 * Returns the raw returned data. To convert to the expected return value,
 * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
 *
 * Requirements:
 *
 * - `target` must be a contract.
 * - calling `target` with `data` must not revert.
 *
 * _Available since v3.1._
 */
 function functionCall(address target, bytes memory data) internal returns (bytes memory) {
 return functionCall(target, data, "Address: low-level call failed");
 }

 /**
 * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
 * `errorMessage` as a fallback revert reason when `target` reverts.
 *
 * _Available since v3.1._
 */
 function functionCall(
 address target,
 bytes memory data,
 string memory errorMessage
 ) internal returns (bytes memory) {
 return functionCallWithValue(target, data, 0, errorMessage);
 }

 /**
 * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
 * but also transferring `value` wei to `target`.
 *
 * Requirements:
 *
 * - the calling contract must have an ETH balance of at least `value`.
 * - the called Solidity function must be `payable`.
 *
 * _Available since v3.1._
 */
 function functionCallWithValue(
 address target,
 bytes memory data,
 uint256 value
 ) internal returns (bytes memory) {
 return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
 }

 /**
 * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
 * with `errorMessage` as a fallback revert reason when `target` reverts.
 *
 * _Available since v3.1._
 */
 function functionCallWithValue(
 address target,
 bytes memory data,
 uint256 value,
 string memory errorMessage
 ) internal returns (bytes memory) {
 require(address(this).balance >= value, "Address: insufficient balance for call");
 require(isContract(target), "Address: call to non-contract");

 (bool success, bytes memory returndata) = target.call{value: value}(data);
 return _verifyCallResult(success, returndata, errorMessage);
 }

 /**
 * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
 * but performing a static call.
 *
 * _Available since v3.3._
 */
 function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
 return functionStaticCall(target, data, "Address: low-level static call failed");
 }

 /**
 * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
 * but performing a static call.
 *
 * _Available since v3.3._
 */
 function functionStaticCall(
 address target,
 bytes memory data,
 string memory errorMessage
 ) internal view returns (bytes memory) {
 require(isContract(target), "Address: static call to non-contract");

 (bool success, bytes memory returndata) = target.staticcall(data);
 return _verifyCallResult(success, returndata, errorMessage);
 }

 /**
 * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
 * but performing a delegate call.
 *
 * _Available since v3.4._
 */
 function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
 return functionDelegateCall(target, data, "Address: low-level delegate call failed");
 }

 /**
 * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
 * but performing a delegate call.
 *
 * _Available since v3.4._
 */
 function functionDelegateCall(
 address target,
 bytes memory data,
 string memory errorMessage
 ) internal returns (bytes memory) {
 require(isContract(target), "Address: delegate call to non-contract");

 (bool success, bytes memory returndata) = target.delegatecall(data);
 return _verifyCallResult(success, returndata, errorMessage);
 }

 function _verifyCallResult(
 bool success,
 bytes memory returndata,
 string memory errorMessage
 ) private pure returns (bytes memory) {
 if (success) {
 return returndata;
 } else {
 // Look for revert reason and bubble it up if present
 if (returndata.length > 0) {
 // The easiest way to bubble the revert reason is using memory via assembly

 assembly {
 let returndata_size := mload(returndata)
 revert(add(32, returndata), returndata_size)
 }
 } else {
 revert(errorMessage);
 }
 }
 }
}
/**
 * @dev Collection of functions related to the address type
 */
function isContract(address account) internal view returns (bool) {
// This method relies on extcodesize, which returns 0 for contracts in
// construction, since the code is only stored at the end of the
// constructor execution.

uint256 size;
assembly {
size := extcodesize(account)
}
return size > 0;
}

/**
 * @dev Returns true if `account` is a contract.
 *
 * [IMPORTANT]
 * ====
 * It is unsafe to assume that an address for which this function returns
 * false is an externally-owned account (EOA) and not a contract.
 *
 * Among others, `isContract` will return false for the following
 * types of addresses:
 *
 * - an externally-owned account
 * - a contract in construction
 * - an address where a contract will be created
 * - an address where a contract lived, but was destroyed
 * ====
 */