Note 4 - Stock Purchase Warrants - Outstanding Stock Purchase Warrants (Details) - shares	Mar. 31, 2023	Dec. 31, 2022
Outstanding warrants (in shares)	450,000	233,333
Warrants Issued with the 2018 Convertible Notes [Member]
Outstanding warrants (in shares)	0	233,333
The 2022 Sales Incentive Warrants [Member]
Outstanding warrants (in shares)	450,000	0