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Comment by wombatpm | Hacker News Reader

There are variations of this style of proof the shows all horses have an infinite number of legs, since horses must have an even number of legs to stand, yet they have two legs in back and forelegs in front, giving them six legs which is an odd number of legs for a horse. The only number that is even and odd is infinity, hence horses have an infinite number of legs.

There is also lemma that since Alexander the Great rode a Black horse, he did not exist, but if he did exist he would have an infinite number of arms and legs

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This is clever, but I wouldn't call it a variation on this style of proof — the OP was an example of a somewhat-subtle logic error, while this is just two instances of wordplay (forelegs ⇔ four legs; six legs being an 'odd' number of legs for a horse).

The joke is funny though

I don't understand. How is that six legs? How is that an odd number? Am I missing a joke?

Six legs on a horse would be very odd indeed

The situation could be much worse.

https://www.penny-arcade.com/comic/2008/05/26/the-unhorse

Wow, I can't believe Penny Arcade is still publishing comics. What a run!

They have an expo too. https://en.wikipedia.org/wiki/PAX_(event)

fourlegs

Yes, it's an English language joke:

Two legs in back, and "forelegs" in front (four-legs). 2 + 4 = 6, which is a peculiar (aka odd) number of legs for a horse to have. Thus horses have both odd and even number of legs, meaning horses have infinite legs.

Actually, the argument was that Alexander the Great had an infinite number of arms. You see, in a famous battle he was forewarned. And as we all know, forewarned is four armed. The rest of the argument is similar.

If this wasn't in Mathematics Made Difficult it should be

It was in "A Stress Analysis of a Strapless Evening Gown", I believe.

Indeed it's there in Joel Cohen, "On the Nature of Mathematical Proofs", pp. 84-90.

(Good recollection!)

Holy moly did I miss the joke

I'm a complete native and fluent English speaker for 30+ years.

Thank you for the explanation - I know others here may need it but, and in all kindness, I'm lmaoing over here being explained this joke like a toddler.

forelegs means "front legs", but also sounds like "four legs". "odd number" means "strange number", and also "number not divisible by 2".

infinity is typically not defined to be even or odd.

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