This space curve in a cube with projections (1b) is a math classic. Use a torch to compare the projections of the space curve (in the center) on a plane with the 3d-printed ones.
This space curve in a cube is a math classic. To view its projections on a plane, just take a torch (or your cell phone lamp).
A trefoil knot is the simplest non-trivial mathematical knot. It has been known for thousands of years.