sympy/sympy — pull request #1181 by goodok (2012-03-27 08:10:15+00:00)
Title: Add the implementation of the incomplite Bell polynomials.

They are also called the second kind of Bell polynomials or "partial"
Bell polynomials. They can be found in Riordan's formulation of di Bruno's
formula for computing an arbitrary order derivative of the composition of
two functions.

P.S.
It's used for series composition.
I gradually begin to transfer the parts of the code from series-prototype necessary in any case.