The Kitties of XNOR

Whoa. Totally sounds like a sci-fi title. I promise there are kittens at the bottom of this post. It’s worth the math for the kittens.

The other night while playing board games, I had an obsessive need to remember what XNOR was for. It is a digital logic gate, but I couldn’t remember it. I was sitting there on the couch, running through OR, NOR, NAND, how to use NOR gates to construct a NAND, the meaning of XOR… but for the life of me, I couldn’t remember XNOR. I know. Good times.

“Exclusive NOR. Exclusive NOR. What could that possibly mean???” I refused the chance to play another game, turned on my cell phone at 11 o’clock at night and spent the next half hour reconstructing my digital logic foundations on the whiteboard in the living room.

XNOR plus gardening lists

This means that the operation is true if both of them are true, OR if both of them are false, but not if only one or the other is true. (I started that sentence with “in plain english”, but after I wrote the rest of the sentence, I deleted that part.)

Anyway. Once I figured this out, I asked my husband, “What is that good for? When would you use an XNOR?” And he said something about it being useful as a logic gate, mathematical calculations, blah blah blah… “No!” I said. (I’m emphatic about math.) “Give me an example of something that is true when both factors are false.” “mumble mumble…” (I got the same answer from a computer scientist the next day.)

And then I discovered the kitties of XNOR. The very next morning, I picked up these guys from the side of the road:

I realized that I was willing to give away both of the kittens. Or neither of the kittens. But I didn’t want to have somebody come and take one of them and leave me with the other. My internal truth-state was an XNOR. And the mystery was solved.

Ha, ha! Digital logic and kitties, together at last. The internet is complete.


No, Mom. I’m not keeping them. My friend the farmer had a surprising need for 2 kittens, and is coming to get them this week.

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6 thoughts on “The Kitties of XNOR

  1. Pingback: Weekend Links

  2. Another practical, everyday application of XNOR: A lightbulb controlled by two switches (often on different floors of a house). The room is dark if both switches are down, or both are up. Either mixed state results in light.

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