Enneagonal antiprismatic prism

The enneagonal antiprismatic prism or eappip is a prismatic uniform polychoron that consists of 2 enneagonal antiprisms, 2 enneagonal prisms, and 18 triangular prisms. Each vertex joins 1 enneagonal antiprism, 1 enneagonal prism, and 3 triangular prisms. As the name suggests, it is a prism based on the enneagonal antiprism. As such it is also a convex segmentochoron.

Vertex coordinates
The vertices of an enneagonal antiprismatic prism, centered at the origin and with edge length 2sin(π/9), are given by the following points, as well as the central inversions of their first three coordinates: where $$H=\sqrt{\frac{1+2\cos\frac\pi9}{2+2\cos\frac\pi9}}\sin\frac\pi9.$$
 * $$\left(1,\,0,\,H,\,±\sin\frac\pi9\right),$$
 * $$\left(\cos\left(\frac{2\pi}9\right),\,±\sin\left(\frac{2\pi}9\right),\,H,\,±\sin\frac\pi9\right),$$
 * $$\left(\cos\left(\frac{4\pi}9\right),\,±\sin\left(\frac{4\pi}9\right),\,H,\,±\sin\frac\pi9\right),$$
 * $$\left(-\frac12,\,±\frac{\sqrt3}2,\,H,\,±\sin\frac\pi9\right),$$
 * $$\left(\cos\left(\frac{8\pi}9\right),\,±\sin\left(\frac{8\pi}9\right),\,H,\,±\sin\frac\pi9\right),$$

Representations
An enneagonal antiprismatic prism has the following Coxeter diagrams:
 * x2s2s9s (full symmetry)
 * x2s2s18o
 * xx xo9ox&#x (enneagonal prism atop gyrated enneagonal prism)