    function execute(Operation calldata _operation) external payable onlyOwnerOrSecurityCouncil {
        bytes32 id = hashOperation(_operation);
        // Check if the predecessor operation is completed.
        _checkPredecessorDone(_operation.predecessor);
        // Ensure that the operation is ready to proceed.
        require(isOperationReady(id), "Operation must be ready before execution");
        // Execute operation.
        _execute(_operation.calls);
        // Reconfirming that the operation is still ready after execution.
        // This is needed to avoid unexpected reentrancy attacks of re-executing the same operation.
        require(isOperationReady(id), "Operation must be ready after execution");
        // Set operation to be done
        timestamps[id] = EXECUTED_PROPOSAL_TIMESTAMP;
        emit OperationExecuted(id);
    }

    /// @notice Executes the scheduled operation with the security council instantly.
    /// @dev Only the security council may execute an operation instantly.
    /// @param _operation The operation parameters will be executed with the upgrade.
    function executeInstant(Operation calldata _operation) external payable onlySecurityCouncil {
        bytes32 id = hashOperation(_operation);
        // Check if the predecessor operation is completed.
        _checkPredecessorDone(_operation.predecessor);
        // Ensure that the operation is in a pending state before proceeding.
        require(isOperationPending(id), "Operation must be pending before execution");
        // Execute operation.
        _execute(_operation.calls);
        // Reconfirming that the operation is still pending before execution.
        // This is needed to avoid unexpected reentrancy attacks of re-executing the same operation.
        require(isOperationPending(id), "Operation must be pending after execution");
        // Set operation to be done
        timestamps[id] = EXECUTED_PROPOSAL_TIMESTAMP;
        emit OperationExecuted(id);
    }

        function _execute(Call[] calldata _calls) internal {
        for (uint256 i = 0; i < _calls.length; ++i) {
            (bool success, bytes memory returnData) = _calls[i].target.call{value: _calls[i].value}(_calls[i].data);
            if (!success) {
                // Propagate an error if the call fails.
                assembly {
                    revert(add(returnData, 0x20), mload(returnData))
                }
            }
        }
    }
