> As easy as it is to make #triangles with #rational #angles, a similar problem in three dimensions proved so challenging that it took decades for the world’s best #mathematicians to resolve. What makes this kind of problem so much harder one dimension up?

#tetrahedron

Why Triangles Are Easy and Tetrahedra Are Hard
https://www.quantamagazine.org/triangles-are-easy-tetrahedra-are-hard-20220131/