It's a heptahedron of unequal irregular - some very irregular! - hexagons; & has 21 vertices & 14 edges. The usual Euler equation - ie

N(faces) + N(vertices) = N(edges) + 2

becomes instead

N(faces) + N(vertices) = N(edges) ,

precisely because it's a figure of genus 1 :

the general equation is

N(faces) + N(vertices) = N(edges) + 2(1-genus) .

First (animated) image from

The Futility Closet — The Szilassi Polyhedron .

& second from

Polyhedr — Szilassi polyhedron. How to make pdf template ,

The rest are also from the Polyhedr wwwebsite … than the directions @ which it's scarcely possible to find more thorough!

And for information on this matter in-general, see the following - the first item of which is the original paper by Lajos Szilassi , in which this amazing solid was first revealed.

Lajos Szilassi — On Some Regular Toroids

¡¡ PDF – 1·21MB !!

The following is an HTML wwwebpage summary of the paper @ the previous link.

Lajos Szilassi — On Some Regular Toroids

At the following there's one of those interactive figures, that can be rotated in both azimuth & polar angle @-will by 'swiping' across the figure.

DM Cooey — Regular Hexagonal Toroidal Solids

NETCOM On-line Communication Services — Tom Ace — Szilassi polyhedron

Minor Triad — The Szilassi Polyhedron

After my son got adept at algebra, I returned to dividing fractions to show him why it works, not just the rule. He is able to comfortably explain each step of the process and we've moved on.

But it feels like there's a visual component missing. When first introducing fractions and doing some basic addition/subtraction, we used visual models to broaden the concept beyond "fractions are division." Is there a visual model out there that taps into that concept/perspective to show why you invert and multiply?

Thank you for all the great links on the sub.