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Note 8 - Stockholders' Equity - Warrants (Details) - USD ($)
 9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Outstanding, number of shares (in shares) 1,592,775  
Outstanding, weighted average exercise price (in dollars per share) $ 2.55  
Outstanding, weighted average remaining life (Year) 2 years 109 days 76 days
Outstanding, intrinsic value  
Issued, number of shares (in shares) 1,749,171  
Issued, weighted average exercise price (in dollars per share) $ 0.50  
Issued, weighted average remaining life (Year) 4 years 127 days  
Issued, intrinsic value $ 560,199  
Exercised, number of shares (in shares) (57,750)  
Exercised, weighted average exercise price (in dollars per share) $ 0.50  
Expired or cancelled, number of shares (in shares)  
Expired or cancelled, weighted average exercise price (in dollars per share)  
Outstanding , number of shares (in shares) 3,284,196 1,592,775
Outstanding , weighted average exercise price (in dollars per share) $ 1.49 $ 2.55
Outstanding, intrinsic value $ 560,199