Enneagrammic antiprismatic prism

The enneagrammic antiprismatic prism or steappip is a prismatic uniform polychoron that consists of 2 enneagrammic antiprisms, 2 enneagrammic prisms, and 18 triangular prisms. Each vertex joins 1 enneagrammic antiprism, 1 enneagrammic prism, and 3 triangular prisms. As the name suggests, it is a prism based on the enneagrammic antiprism. Being a prism based on an orbiform polytope, it is also a segmentochoron.

Vertex coordinates
The vertex coordinates of an enneagrammic antiprismatic prism with edge length 2sin(2π/9) are given by: where $$H=\sqrt{\frac{1+2\cos\frac{2\pi}9}{2+2\cos\frac{2\pi}9}}\sin\frac{2\pi}9.$$
 * $$\left(1,\,0,\,±H,\,±\sin\frac{2\pi}9\right),$$
 * $$\left(\cos\left(\frac{2\pi}{9}\right),\,±\sin\left(\frac{2\pi}{9}\right),\,±H,\,±\sin\frac{2\pi}9\right),$$
 * $$\left(\cos\left(\frac{4\pi}{9}\right),\,±\sin\left(\frac{4\pi}{9}\right),\,±H,\,±\sin\frac{2\pi}9\right),$$
 * $$\left(-\frac12,\,±\frac{\sqrt3}{2},\,±H,\,±\sin\frac{2\pi}9\right),$$
 * $$\left(\cos\left(\frac{8\pi}{9}\right),\,±\sin\left(\frac{8\pi}{9}\right),\,±H,\,±\sin\frac{2\pi}9\right),$$

Representations
An enneagrammic antiprismatic prism has the following Coxeter diagrams:
 * x2s2s18/2o (full symmetry)
 * x2s2s9/2s
 * xx xo9/2ox&#x (enneagrammic prism atop enneagrammic prism)