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Note 8 - Warrants (Tables)
12 Months Ended
Dec. 31, 2020
Notes Tables  
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]
   

Year Ended December 31, 2020

    Year Ended December 31, 2019  
   

Shares

   

Wtd. Avg.

Exercise Price

   

Shares

   

Wtd. Avg.

Exercise Price

 

Outstanding at beginning of year

    3,959,005     $ 4.33       4,080,005     $ 4.35  

Exercised

    (3,879,905 )     4.33       (121,000 )     4.75  

Outstanding and exercisable at end of year

    79,100     $ 4.75       3,959,005     $ 4.33