DILOG _ _ _ _ _ _ _ _ _ _ _ _ operator

The dilog operator is known to the differentiation and integration operators, but has numeric value attached only at dilog(0). Dilog is defined by

dilog(x) = -int(log(x),x)/(x-1)

examples:

df(dilog(x**2),x); 

           2
    2*LOG(X )*X
  - ------------
       2
      X   - 1



int(dilog(x),x); 

  DILOG(X)*X - DILOG(X) + LOG(X)*X - X 



dilog(0); 

    2
  PI
  ----
   6