## 3 Results
### Lean
#### 3.3.8 The Interaction between Lean Production and Industry 4.0  
Lean production is a key characteristic of the 3 rd industrial revolution production systems. While other aspects have evolved (e.g., technology, from computers to smart digital devices) or radically changed (e.g., market focus from variety and lead time to customization and personalization), Lean is still up-to-date in the era of Industry 4.0 [11]. Moreover, the relationship between Lean and Industry 4.0 technologies is catching increasing attention from academia in the last decade [163].  
The question posed by [PERSON] et al. [164] has been addressed by many authors, both theoretically and analyzing use cases across many countries: \"Can Lean and Industry 4.0 coexist and support each other, and if so, how?\" There are four main lines of thought when answering this question: (1) Lean techniques and Industry 4.0 technologies interact in a positive way, and there are many cases to illustrate this [8; 9; 165; 166]; (2) Lean facilitates the change towards Industry 4.0 [167; 168]; (3) Industry 4.0 supports Lean, i.e., makes the factory Lean [169; 170; 171; 172; 173]; (4) although Lean and Industry 4.0 aim for the same goals, their approach is essentially different regarding digital technology [174].  
Five articles looked at answering [PERSON] et al.'s question [164] by surveying the industrial reality of different countries, all of them finding positive interactions between Lean and Industry 4.0 technologies. [PERSON] et al. analyzed 260 industrial companies in Germany and found Lean as an enabler of Industry 4.0 [168]. [PERSON] et al. looked into 110 user cases in Brazil and found a positive Lean-Industry 4.0 correlation, as well as increased benefits of new digital technologies where Lean was also present [175]. [PERSON] et al. analyzed 108 cases of European manufacturers, concluding that Lean allows achieving higher levels of Industry 4.0 while lacking Lean production techniques makes it more difficult to change towards Industry 4.0 [176]. [PERSON] et al. investigated 200 cases in Italy and foundthat most strategic, operational areas benefit from implementing Industry 4.0, such as design-to-cost, supply chain integration or machinery-electronics-database integration [177]. [PERSON] et al. analyzed user cases in Switzerland and found that Lean maturity allows greater performance improvements from implementing Industry 4.0 [178].  
**In conclusion**, there is a wealth of evidence showing that Lean manufacturing is a valid approach to improve assembly operation in the context of mass customization and that Lean and Industry 4.0 can benefit from synergies because each one enhances the other. However, according to some authors [174], Industry 4.0 and Lean have essentially different approaches regarding the role digital technologies should have.  
While some authors deem that [PERSON] considers robots, machines and computers in the opposing side of _jidoka_ (\"automation with a human touch\"), it should be noted that the lack of enthusiasm of [PERSON] towards digital technologies could have been influenced by the current digital technologies of that era (the 1950s-1980s). Since the rate of change in digital technology has been particularly remarkable in the past four decades, it seems bold to assume that [PERSON]'s views on computers in the second half of the 20 th century still apply.