  The main result of this paper is the construction of a bijection of the set
of words in so-called standard order of length $n$ formed by four different
letters and the set $\mathbb{N}^n$ of all subspaces of a fixed $n$-dimensional
maximal isotropic subspace of the $2n$-dimensional symplectic space $V$ over
$\mathbb{F}_2$ which are not maximal in a certain sense. Since the number of
different words in standard order is known, this gives an alternative proof for
the formula of the dimension of the universal embedding of a symplectic dual
polar space $\mathcal G_n$. Along the way, we give formulas for the number of
all $n$- and $(n-1)$-dimensional totally isotropic subspaces of $V$.
