  We study Z2 orbifolds of M-theory in terms of E10. We find a simple relation
between the Z2 action on E10 and the imaginary root that corresponds
[hep-th/0401053] to the "twisted sector" branes. We discuss the connection
between the Kac-Moody algebra DE10 and the "untwisted" sector, and we
demonstrate how DE18 can describe both the untwisted and twisted sectors
simultaneously.
