function removePermission($resource, $permission) {
SecurityGroup::requirePermission("CHANGE");
$group_id = $this->getId();
$resource_id = $resource->getId();
$permission_id = $permission->getId();
$sql = "DELETE FROM security_group_permission
WHERE group_id = ".Database::sqlValue($group_id)."
AND resource_id = ".Database::sqlValue($resource_id)."
AND permission_id = ".Database::sqlValue($permission_id);
Database::query($sql);
}
