trim between lines(gap one side).
 
  File name : TRIMB3.LSP

  When we work with steel drawing, We frequently have to zoom in and zoon out, because steel plate is very thin.
This program had been made to avoid that bothers.
We must make a gap of 30mm between lower flange and vertical stiffener of Steel Box girder bridge. 
This program make that gap. Select just two point(p1 and p2 on below image). Program makes gap.


 
   Example
  Offset distance <30> : 30    [Enter gap distance. 30mm in this case]
  Select first point: {p1}              [Pick first point to select plate lies]
  Select second point: {p2}             [Pick second point]