# Dx number (InstanceTopic, 3)

### From Hi.gher. Space

A **Dx number** is a number representing the mirror selection on straight Coxeter-Dynkin symbols. The Dx number acts as a bitfield, where the zeroth bit corresponds to the leftmost mirror, the first bit to the 2nd mirror from the left, etc. A bit is clear if the mirror is inactive ("o"), and set if the mirror is active ("x"). The Dx number of an n-dimensional polytope is always between 0 and 2^{n}-1 inclusive.