= Antiprism
An $n$-gonal antiprism is a <polyhedron> with two parallel congruent $n$-gon bases, one rotated relative to the other, and a band of $2n$ triangular side faces joining them. For the usual convex regular realization, both bases are regular and all side triangles are <equilateral triangles>.
Its combinatorial counts are $V=2n$, $E=4n$, and $F=2n+2$: the bases contribute $2n$ edges and the zigzag side band another $2n$. Hence $V-E+F=2$, agreeing with <Euler characteristic>. A triangular antiprism is an <octahedron>; a square antiprism has eight vertices, two square bases and eight triangular side faces.
A <prism> instead joins corresponding base vertices with a band of quadrilateral faces. The relative rotation and triangular band are the defining differences in the antiprism construction.
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