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Activities in allowance for doubtful accounts (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Statement of Financial Position [Abstract]    
Balance at Beginning of Year $ 40,651 $ 89,058
Charged to Costs and Expenses
Amounts Written Off (48,407)
Balance at End of Year $ 40,651 $ 40,651