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Inventory (Details) - USD ($)
Nov. 30, 2018
May 31, 2018
Inventory Disclosure [Abstract]    
Raw materials $ 709,862 $ 726,852
Work-in-process 10,806,618 9,990,225
Finished goods 665,245 700,698
Gross inventory 12,181,725 11,417,775
Less allowance for obsolescence 100,000 100,000
Net Inventory $ 12,081,725 $ 11,317,775