Wow! What an exercise in irony. I just read my own post. I spent three paragraphs explaining the virtue of simplicity. Please forgive me and let me try this one more time.

You (Kai and Raghunathan) are pointing out that in order to solve for two unknowns one needs two independent equations. I am saying that, for the purpose of this riddle, truth (and by extention the mutually exclusive lie) is a constant instead of a variable. Thus, the system of equations is reduced to a single equation and a single unknown.

Or maybe it really is a poor riddle.