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Note 4 - Accounts Receivable (Tables)
 9 Months Ended
Sep. 30, 2019
Notes Tables  
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
   
September 30,
    
December 31,
  
   
2019
    
2018
  
                 
Accounts receivable - current
   $
787,119
     $
1,587,817
  
Accounts receivable - non current
    
1,720,000
      
1,720,000
  
Total accounts receivable
    
2,507,119
      
3,307,817
  
Allowance for doubtful accounts - current
    
(13,785
)
    
(13,785
)
Allowance for doubtful accounts - non current
    
(1,720,000
)
    
(1,720,000
)
Total allowance for doubtful accounts
    
(1,733,785
)
    
(1,733,785
)
Accounts receivable, net of allowance for doubtful accounts
   $
773,334
     $
1,574,032