Proof of an impossibility.
     It gives us a new idea of constructing.
     It clarifies our idea of constructing.
     An idea getting clearer.
     Impossibility of making coincide right & left hand.
     How does the ‘proof’ convince us of the
impossibility? As an experiment would? Can't he still look for a construction of the trisection? Certainly but the point of it has been removed for him.