Change a part of line to hidden line.
 
  Program name : BDASH.LSP

  When you draw a structure, the structure sometimes crosses up and down. In that case, the bottom structure line 
is invisible and must be represented by a dashed line. With this program, you only need to select lines and pick breaking point.
You don't need to trim lines and redraw line with hidden line type. 
again . 

 
 Example
Select Line: {p1}               [Select line]
First point: int of {p2}        [Pick start point to be brocken]
Second point: int of {p3}       [Pick end point to be brocken]
command:                       [Type Enter to repeat command]
Select Line: {p4}               [Select line]
First point: int of {p5}        [Pick start point to be brocken]
Second point: int of {p6}       [Pick end point to be brocken]