Comment by ianstormtaylor | Hacker News Reader

Comment by ianstormtaylor | Hacker News Reader

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That's a really nice mental model for it.

I learned a similar concept in Typography class... for an assignment to design a new number. I was a little indecisive and apologized when I showed up to critique with two different number drawings [0]. My professor (Cyrus Highsmith [1]) looked at them and said not to worry because they were the same number anyways. I didn't get it at first, but a few minutes after sitting back down I realized what he meant, and it's stuck with me ever since.

Using the 7-segment display as an example would have been a great way to explain the concept to me at the time. I'll remember that for next time!

Also a cool way to think about it, because it begs the question of which 7-segment permutations don't map to existing symbols, for whenever someone needs to design a new one in the future.

[0]: https://i.imgur.com/8zB44gi.png

[1]: https://en.wikipedia.org/wiki/Cyrus_Highsmith

One thing which obviously cuts down the code space of 7 segments is the fact that there's no levitating glyphs. They all touch the floor somehow. Another thing that cuts down on the code space is the fact that there's no disconnected glyphs. All the segments touch at least one other segment. I suppose you could write 11 on a single 7 seg display, but you wouldn't think of 11 as a single character. The last restriction that cuts things down a tiny bit is that for vertical line characters (i,l,1), it doesn't matter if you use the segments on the left or the right. They are still the same character.

Applying these constraints, There are a handful of could-be letters left over. Some are already in use like the upside down A (used in mathematics), Capital Gamma, entailment symbol (used in logic). Others, like upside down and/or backwards F, upside down 4, and -| aren't used anywhere AFAIK.

To save others from looking it up:

upside down A: ∀

Capital Gamma: Γ

Entailment symbol: ⊧

That last one would also be hard to represent in a 7 segment display, perhaps that would be the upside down F

The other entailment symbol. ⊢. Sometimes called "the turnstile".

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