contract Ownable {
  address private _owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor () internal {
      _owner = msg.sender;
      emit OwnershipTransferred(address(0), _owner);
  }

  /**
   * @return the address of the owner.
   */
  function owner() public view returns (address) {
      return _owner;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
      require(isOwner());
      _;
  }

  /**
   * @return true if `msg.sender` is the owner of the contract.
   */
  function isOwner() public view returns (bool) {
      return msg.sender == _owner;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
      _transferOwnership(newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address newOwner) internal {
      require(newOwner != address(0));
      emit OwnershipTransferred(_owner, newOwner);
      _owner = newOwner;
  }

}
/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
function owner() public view returns (address) {
      return _owner;
  }
/**
 * @return the address of the owner.
 */