Note 11 - Stock Options and Incentive Plans - Restricted Stock Options Activity (Details) - $ / shares	9 Months Ended
	Jan. 31, 2022	Apr. 30, 2021
Outstanding, shares (in shares)	7,500,000
Outstanding, weighted average fair value (in dollars per share)	$ 0.40	$ 0.40
Outstanding, shares (in shares)	7,400,000
Restricted Stock Options, Vesting April 2024 [Member]
Forfeited, shares (in shares)	(50,000)
Forfeited, weighted average fair value (in dollars per share)	$ 0.40
Restricted Stock Options, Vesting March 2025 [Member]
Forfeited, shares (in shares)	(50,000)
Forfeited, weighted average fair value (in dollars per share)	$ 0.40