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Common stock and convertible preferred stock (Tables)
12 Months Ended
Dec. 31, 2020
Common stock and convertible preferred stock  
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]

June 2, 2020

    

October 6, 2020

 

Volatility rate

 

79.0

%  

82.0

%

Risk-free interest rate

 

0.2

%  

0.2

%

Expected term (in years)

 

3.0

 

2.7

Strike price (per share)

$

9.00

$

9.00

Fair value of Series A convertible preferred stock

$

4.44

$

12.00