 Usage:  {lt, pt} = contour2 (x, c)  
 
 Input:

  x                      n x 3 matrix 
                         
  c                      scalar 
                         
 Output:

  lt                     m1 x 2 line matrix 
                         
  pt                     m2 x 2 point matrix 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
