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Summary of significant accounting policies - Estimated useful lives of intangible assets (Details)
12 Months Ended
Dec. 31, 2021
Software | Maximum  
Finite-Lived Intangible Asset, Useful Life 10 years
Software | Minimum  
Finite-Lived Intangible Asset, Useful Life 5 years
Land use right  
Finite-Lived Intangible Asset, Useful Life 50 years
Patents  
Finite-Lived Intangible Asset, Useful Life 10 years