Grassmann algebra (see, for example [5] for a general reference) is extensively used in
mathematical physics to describe fermions, which are elementary particles obeying the
so-called Fermi-Dirac statistics. The generators of the algebra are called Grassmann
variables and they obey anti-commuting relations (unlike real or complex variables,
which obey commuting relations, and which are used in mathematical physics to describe bosons). One can then define the so-called Grassmann integral, which is a linear
form on the Grassmann algebra.
The rules of Grassmann calculus lead to very interesting developments outside the
original field of mathematical physics. Thus, in combinatorics, Grassmann algebra is
used to derive elegant expressions for determinants and Pfaffians. These expressions
have already been used to prove the contraction-deletion formula of the Tutte and