  A symmetric bilinear form on a certain subspace $\widehat{\mathbb T}^{\bf b}$
of a completion of the Fock space $\mathbb T^{{\bf b}}$ is defined. The
canonical and dual canonical bases of $\widehat{\mathbb T}^{\bf b}$ are dual
with respect to the bilinear form. As a consequence, the inversion formula
connecting the coefficients of the canonical basis and that of the dual
canonical basis of $\widehat{\mathbb T}^{\bf b}$ expanded in terms of the
standard monomial basis of $\mathbb T^{{\bf b}}$ is obtained. Combining with
the Brundan's algorithm for computing the elements in the canonical basis of
$\widehat{\mathbb{T}}^{{\bf b}_{\mathrm{st}}}$, we have an algorithm computing
the elements in the canonical basis of $\widehat{\mathbb{T}}^{{\bf b}}$ for
arbitrary ${\bf b}$.
