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Note 3 - Basis of Presentation and Summary of Significant Accounting Policies (Tables)
12 Months Ended
Dec. 31, 2020
Notes Tables  
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]
   
December 31,
 
   
2020
   
2019
 
Common stock warrants
   
9,100,112
     
22,385,141
 
Stock options
   
2,240,204
     
309,276
 
     
11,340,316
     
22,694,417