Quarterly report pursuant to Section 13 or 15(d)

Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details)

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Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details) - Stock Purchase Warrants [Member]
9 Months Ended
Sep. 30, 2019
$ / shares
shares
Number of warrants outstanding (in shares) | shares 8,018,903
Range One [Member]  
Lower exercise price range (in dollars per share) $ 0.0001
Upper range of exercise prices (in dollars per share) $ 0.0001
Number of warrants outstanding (in shares) | shares 1,048,166
Expiration dates perpetual
Range Two [Member]  
Lower exercise price range (in dollars per share) $ 2.19
Upper range of exercise prices (in dollars per share) $ 2.70
Number of warrants outstanding (in shares) | shares 6,538,035
Range Two [Member] | Minimum [Member]  
Expiration dates December 2020
Range Two [Member] | Maximum [Member]  
Expiration dates August 2024
Range Three [Member]  
Lower exercise price range (in dollars per share) $ 3.38
Upper range of exercise prices (in dollars per share) $ 17.50
Number of warrants outstanding (in shares) | shares 406,223
Range Three [Member] | Minimum [Member]  
Expiration dates October 2023
Range Three [Member] | Maximum [Member]  
Expiration dates July 2024
Range Four [Member]  
Lower exercise price range (in dollars per share) $ 22.20
Upper range of exercise prices (in dollars per share) $ 782.60
Number of warrants outstanding (in shares) | shares 26,479
Range Four [Member] | Minimum [Member]  
Expiration dates October 2019
Range Four [Member] | Maximum [Member]  
Expiration dates July 2023