  It is well known that many geometric properties of Schubert varieties of type
$A$ can be interpreted combinatorially. Given two permutations $w,x\in S_n$ we
give a combinatorial consequence of the property that the smooth locus of the
Schubert variety $X_w$ contains the Schubert cell $Y_x$. This is a necessary
ingredient for the interpretation of recent representation-theoretic results of
the author with M\'inguez in terms of identities of Kazhdan--Lusztig
polynomials.
