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Note 4 - Accounts Receivable (Tables)
 12 Months Ended
Dec. 31, 2020
Notes Tables  
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
   
2020
    
2019
  
Accounts receivable
   $
3,989,200
     $
2,446,486
  
                 
Provision for doubtful accounts
    
(55,660
 )    
(53,708
 )
                 
Net accounts receivable
   $
3,933,540
     $
2,392,778