  We prove a generalization of Quillen's Theorem B to strict
$\infty$-categories. More generally, we show that under similar hypothesis as
for Theorem B, the comma construction for strict $\infty$-categories, that we
introduced with Maltsiniotis in a previous paper, is the homotopy pullback with
respect to Thomason equivalences. We give several applications of these
results, including the construction of new models for certain Eilenberg-Mac
Lane spaces.
