$0  file1 file2 file3 file4 

    Performs similar things to draw the venn diagram for 4 sets. 
    Each file given is regarded as a set that consists of 
    the elements; an element is a character string separated by
    line ending characters.  The venn diagram can be drawn 
    using 4 rectangles or 4 ovals so this program utilizes this 
    mathematical theorem.

   Options : 
     -= : skip reading the first line of every 4 files.
     -b : skip blank lines.
     -x : Also adds 10 x 10 table to the ouput. You can easily understand it.