Tractrix With Dog Leash Construction
The "Moving Plane" Attached To The Leash Draws Related Curves

The tractrix family is defined by these equations:
  c(t) = [stick*sin(t), stick*cos(t) + log(tang(t/2))].
  The default is stick = 1 for the tractrix itsself.
These curves are obtained with tangents. For the simplest such construction see: Cycloid.
The caustic of the normals of the tractrix is the Catenary.