Grassmannian
Grassmannian(k,r,R) or Grassmannian(k,r) -- given natural numbers
k <= r,
and optionally a ring R with at least binomial(r+1,k+1)
variables, the routine defines the ideal of the
Grassmannian of projective k-planes in P^r, using
the first binomial(r+1,k+1) variables of R.
If R is not given, the routine makes and uses
ZZ/31991[vars(0..binomial(r+1,k+1)-1].
