  Polynomial solutions to the KP hierarchy are known to be parametrized by a
cone over an infinite-dimensional Grassmann variety. Using the notion of
Schubert derivation on a Grassmann algebra, we encode the classical Pl\"ucker
equations of Grassmannians of r-dimensional subspaces in a formula whose limit
for $r\rightarrow\infty$ coincides with the KP hierarchy phrased in terms of
vertex operators.
