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Income Taxes Carryforward (Details) - USD ($)
12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Tax Credit Carryforward    
Valuation allowance $ 17,453,000 $ 14,149,000
Increase in valuation allowance 3,304,000 $ 2,871,000
State    
Tax Credit Carryforward    
Tax credit carryforwards 28,530,000  
IRS    
Tax Credit Carryforward    
Tax credit carryforwards $ 2,260,000