 Usage:  (sig)=sigma(et,a1,g1,c0,os,hndl)  
 
 Input:

  et                     
                         
  a1                     
                         
  g1                     
                         
  c0                     
                         
  os                     
                         
  hndl                   
                         
 Output:

  sig                    
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
