impossibility proof, n.All

An Impossibility proof (n.) carries ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠a prediction: don't exert yourself trying to trisect the angle; it cannot be done.