Editing Tetrahedron (section)

=== Helical stacking ===
[[File:600-cell tet ring.png|thumb|A single 30-tetrahedron ring [[Boerdijk–Coxeter helix]] within the [[600-cell]], seen in stereographic projection]]
Regular tetrahedra can be stacked face-to-face in a [[chiral]] aperiodic chain called the [[Boerdijk–Coxeter helix]].

In [[Four-dimensional space|four dimensions]], all the convex [[regular 4-polytope]]s with tetrahedral cells (the [[5-cell#Boerdijk–Coxeter helix|5-cell]], [[16-cell#Helical construction|16-cell]] and [[600-cell#Union of two tori|600-cell]]) can be constructed as tilings of the [[3-sphere]] by these chains, which become periodic in the three-dimensional space of the 4-polytope's boundary surface.
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