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Note 9 - Stock-based Compensation - Allocation of Stock Option Expense (Details) - Employee Stock Option [Member] - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Allocated stock option expense $ 57,224 $ 54,805 $ 67,905
General and Administrative Expense [Member]      
Allocated stock option expense 31,271 31,191 45,822
Research and Development Expense [Member]      
Allocated stock option expense $ 25,953 $ 23,614 $ 22,083