tetrahedron

Furthermore, in 1980 Hans Debrunner showed that any tetrahedron that tiles space must have a Dehn invariant of 0 — the same as a cube.

The tetrahedron is the simplest three-dimensional shape with flat sides.

It establishes that there are exactly 59 isolated examples plus two infinite families of tetrahedra that meet this condition.

On the cube, tetrahedron, octahedron and icosahedron, any straight path that starts and ends on the same vertex must pass through some other vertex along the way.

Imagine starting from a vertex of a tetrahedron and heading out on a straight path along a face.

Kailas turns a sharp edge to the north, and from here the peak resembles a tetrahedron more than ever.

The most simple of all would have been the tetrahedron, or pyramid built upon a triangular base.

At the vertices of a regular tetrahedron may be found such points.

Above the tetrahedron is a balloon-shaped figure, apparently drawn into shape by the attraction of the tetrahedron.

This puzzle concerns the painting of the four sides of a tetrahedron, or triangular pyramid.