## 2 Literature Review  
### Lean Manufacturing as the Foundation of Lean Maintenance  
Global industry in the 21 st century motivates companies to seek and implement a more competitive production system. Many of them implement or plan to implement lean manufacturing. Lean manufacturing philosophy is mainly used in industry to increase efficiency and productivity. It was developed in the 1990s and is mainly based on the Toyota Production System (TPS) [19]. The basis of this concept is the elimination of unnecessary losses that have a significant impact on productivity and profit. These losses can be divided into three main types: Muda, Mura, and Muri. Muda identifies seven types of waste, which include transportation, supplies, redundant movement, waiting, overproduction, over processing, and defects. Mura means unevenness, non-uniformity, and irregularity and is the reason for the existence of any of the seven wastes. Finally, Muri means overburden, beyond one's power, excessiveness, impossible, or unreasonableness and can result from Mura and, in some cases, can be caused by excessive removal of Muda from the process [20; 21; 22]. Production using the lean manufacturing philosophy should consist of reducing the amount of losses related to people, inventory, time to market, and production space, so as to obtain a highly reactive demand for customer needs, while producing high-quality products in the most efficient and cost-effective manner [23]. Lean manufacturing can be a cost reduction mechanism, and if properly implemented, it will make it a world-class organization [24], and importantly, lean manufacturing can be used in all industries [19; 25]. Many organizations have embarked on the practice of using \"lean tools\" primarily to eliminate wasted production. It is widely recognized that organizations that have applied lean manufacturing methods have significant cost and quality advantages over those that continue to use traditional manufacturing [23]. It turns out that organizations pay more and more attention to maintenance, which is why some organizations have started to practice lean maintenance in addition to lean manufacturing. Lean maintenance is a concept that implements activities aimed at increasing the effectiveness of technical infrastructure. These activities are related to the elimination of losses in maintenance, such us [18; 19]:  
* Unproductive works--execution of works that do not increase the reliability of the technical infrastructure;
* Delays in the implementation of works--waiting for the availability of technical infrastructure in order to carry out preventive actions;
* Unnecessary motion--unnecessary trips to stores with spare parts and searching for the required tools to get the job done;
* Poor inventory management--lack of having an appropriate number of needed spare parts in a specific time;
* Reworking--repeating tasks due to poor quality of performance;
* Insufficient use of resources--inadequate use of available resources and skills of maintenance teams;
* Machine misuse--malfunction or intentional operating strategies leading to maintenance work that does not need to be performed;
* Ineffective data management--collecting data that are useless, and not those that are important. [PERSON] et al. [26] show the connection between the sources of waste in lean manufacturing and lean maintenance (Table 1). The elimination of waste is most often carried out by implementing lean tools such as 5S, standardized work, Kaizen, Poka-Yoke, and value stream mapping (VSM) [27; 28]. They are most commonly applied to make production processes more effective and to reduce lead-time or cost of