Annual report pursuant to Section 13 and 15(d)

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

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Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details)
12 Months Ended
Dec. 31, 2018
$ / shares
shares
Number of warrants outstanding (in shares) | shares 7,077,374
Stock Purchase Warrants [Member] | Range One [Member]  
Lower exercise price range (in dollars per share) $ 0.57
Upper range of exercise prices (in dollars per share) $ 0.875
Number of warrants outstanding (in shares) | shares 6,162,709
Stock Purchase Warrants [Member] | Range Two [Member]  
Lower exercise price range (in dollars per share) $ 1.11
Upper range of exercise prices (in dollars per share) $ 5.79
Number of warrants outstanding (in shares) | shares 34,617
Stock Purchase Warrants [Member] | Range Three [Member]  
Lower exercise price range (in dollars per share) $ 12.80
Upper range of exercise prices (in dollars per share) $ 12.90
Number of warrants outstanding (in shares) | shares 39,296
Stock Purchase Warrants [Member] | Range Four [Member]  
Lower exercise price range (in dollars per share) $ 16.20
Upper range of exercise prices (in dollars per share) $ 16.30
Number of warrants outstanding (in shares) | shares 174,544
Stock Purchase Warrants [Member] | Range Six [Member]  
Lower exercise price range (in dollars per share) $ 22.10
Upper range of exercise prices (in dollars per share) $ 27.90
Number of warrants outstanding (in shares) | shares 153,755
Stock Purchase Warrants [Member] | Range Seven [Member]  
Lower exercise price range (in dollars per share) $ 34.50
Upper range of exercise prices (in dollars per share) $ 39.20
Number of warrants outstanding (in shares) | shares 236,556
Stock Purchase Warrants [Member] | Range Nine [Member]  
Lower exercise price range (in dollars per share) $ 47.30
Upper range of exercise prices (in dollars per share) $ 52.20
Number of warrants outstanding (in shares) | shares 275,897