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Significant accounting policies (Tables)
 12 Months Ended
Dec. 31, 2019
Significant accounting policies  
Summary of useful lives of assets

 

 

 

 

    

Useful

 

 

Life (years)

Improvement in leased assets

 

20

Machinery and equipment

 

10

Furniture and office equipment

 

10

Transportation equipment

 

4

Computer equipment

 

3.3