15.44.6  HIDE 

Controls whether hidden lines are drawn for a 3-d  mesh,  or  whether  one
histogram  hides the next.  HIDE=OFF draws the hidden lines, while HIDE=ON
omits them.
(Default:HIDE=ON for mesh, HIDE=OFF for data)

This  works  very well for curves which are functions of x, or curves that 
have at most 2 y values for a given x.  Curves with more than 2  y  values
per X will hide the entire region from the minimum to the maximum y.