 Usage:  bitree(vers,task)  
 
 Input:

  vers                   scalar: (=0) - european option, (=1) - american option 
                         
  task                   scalar: (=1) - without dividend, (=2) - with 
                         continuously paid dividend, (=3) - in % 
                         of the stock value", (=4) - with a fixed 
                         dividend at the end of T, (=5) - if for 
                         exchange rate 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
