Triangular-enneagonal duoprism

The triangular-enneagonal duoprism or tedip, also known as the 3-9 duoprism, is a uniform duoprism that consists of 3 enneagonal prisms and 9 triangular prisms, with two of each at each vertex. It can also be seen as a convex segmentochoron, being an enneagon atop an enneagonal prism.

This polychoron can be subsymmetrically faceted into a 9-3 step prism, although it cannot be made uniform.

Vertex coordinates
The vertex coordinates of a triangular-enneagrammic duoprism, centered at the origin and with edge length 2sin(π/9), are given by: where j = 2, 4, 8.
 * $$\left(0,\frac{2\sqrt3}3\sin\frac{\pi}9,1,0\right),$$
 * $$\left(0,\frac{2\sqrt3}3\sin\frac{\pi}9,\cos\left(\frac{j\pi}9\right),±\sin\left(\frac{j\pi}9\right)\right),$$
 * $$\left(0,\frac{2\sqrt3}3\sin\frac{\pi}9,-\frac12,±\frac{\sqrt3}2\right),$$
 * $$\left(±\sin\frac{\pi}9,-\frac{\sqrt3}3\sin\frac{\pi}9,1,0\right),$$
 * $$\left(±\sin\frac{\pi}9,-\frac{\sqrt3}3\sin\frac{\pi}9,\cos\left(\frac{j\pi}9\right),±\sin\left(\frac{j\pi}9\right)\right),$$
 * $$\left(±\sin\frac{\pi}9,-\frac{\sqrt3}3\sin\frac{\pi}9,-\frac12,±\frac{\sqrt3}2\right),$$