library Roles {
struct Role {
mapping (address => bool) bearer;
}

/**
* @dev give an account access to this role
*/
function add(Role storage role, address account) internal {
require(account != address(0));
require(!has(role, account));

role.bearer[account] = true;
}

/**
* @dev remove an account's access to this role
*/
function remove(Role storage role, address account) internal {
require(account != address(0));
require(has(role, account));

role.bearer[account] = false;
}

/**
* @dev check if an account has this role
* @return bool
*/
function has(Role storage role, address account) internal view returns (bool) {
require(account != address(0));
return role.bearer[account];
}
}
/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
function has(Role storage role, address account) internal view returns (bool) {
require(account != address(0));
return role.bearer[account];
}
/**
 * @dev check if an account has this role
 * @return bool
 */