  We give a new characterization of Littlewood-Richardson-Stembridge tableaux
for Schur $P$-functions by using the theory of $\mf{q}(n)$-crystals. We also
give alternate proofs of the Schur $P$-expansion of a skew Schur function due
to Ardila and Serrano, and the Schur expansion of a Schur $P$-function due to
Stembridge using the associated crystal structures.
