The curvature and torsion: how to distinguish the shape of a curve 
Still curvature and torsion
The curve in the picture below (constructed with 2D app) cannot be constructed with 3D app (\(k>0\)).
This curve is just an example, since there is an infinity of curves with this property. In fact, whenever the curvature of the curve take positive and negative values, it will not be possible to reproduce it in the three-dimensional case (where the curvature is always greater than zero).
