def remove_from_set(set, item)
      Predictor.redis.multi do |redis|
        redis.srem(redis_key(:items, set), item)
        redis.srem(redis_key(:sets, item), set)
      end
    end
def remove_from_set(set, item)
      Predictor.redis.multi do |redis|
        redis.srem(redis_key(:items, set), item)
        redis.srem(redis_key(:sets, item), set)
      end
    end
Delete a specific relationship