Quarterly report pursuant to Section 13 or 15(d)

7. STOCKHOLDERS' EQUITY (Details)

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7. STOCKHOLDERS' EQUITY (Details)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
STOCKHOLDERS' EQUITY    
Expected term   6 years 3 months 18 days
Expected term, minimum 5 years 9 months 18 days  
Expected term, maximum 6 years 3 months 18 days  
Volatility 61.00% 61.00%
Dividend yield 0.00% 0.00%
Risk-free interest rate   2.59%
Risk-free interest rate, minimum 2.25%  
Risk-free interest rate, maximum 2.63%