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Accounts payable trade and other accrued liabilities (Tables)
12 Months Ended
Dec. 31, 2019
Trade and other payables [abstract]  
Schedule of Accounts payable trade and other accrued liabilities
December 31,
  2 0 1 9   2 0 1 8
           
Trade accounts payable $ 4,179,830   $ 4,390,413
Other accrued liabilities   1,547,214     2,057,557
  $ 5,727,044   $ 6,447,970