 Usage:  gs = grcontour3 (x, c, {, col})  
 
 Input:

  x                      n x 4 matrix 
                         
  c                      m x 1 vector 
                         
  col                    m x 1 color 
                         
 Output:

  gs                     composed graphical object 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
