  We clarify the relations between sewing and propagating conformal blocks. In
particular, we show that sewing and propagation and commuting procedures. As an
application, we give a geometric construction of permutation-twisted modules
for tensor product VOAs. Their first (algebraic) construction is due to
Barron-Dong-Mason.
  The results and the point of view in this article are crucial for relating
the (genus-0) permutation-twisted conformal blocks associated to a tensor
product VOA $V^{\otimes k}$ and the untwisted conformal blocks (of possibly
higher genera) associated to $V$, which will be discussed in an upcoming work.
