library/Rediska/Key/Set.php
public function diff($setOrSets, $storeKeyName = null)
    {
        $sets = $this->_prepareSetsForCompare($setOrSets);

        return $this->_getRediskaOn()->diffSets($sets, $storeKeyName);
    }
public function diff($setOrSets, $storeKeyName = null)
    {
        $sets = $this->_prepareSetsForCompare($setOrSets);

        return $this->_getRediskaOn()->diffSets($sets, $storeKeyName);
    }
Return the difference between the Sets

@param string|array $setOrSets    Set key name or object, or array of its
@param string|null  $storeKeyName Store union to set with key name
@return array|boolean