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Note 9 - Fair Value of Financial Instruments (Tables)
9 Months Ended
Sep. 30, 2021
Notes Tables  
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
  

Fair Value Measurements of Level 3 liability-classified warrant

 

Warrant liability at December 31, 2020

 $6,639,211 

Decrease in fair value of warrant liability

  (294,548)

Exercise of warrants

   

Warrant liability at September 30, 2021

 $6,344,663