This afternoon, my wife suddenly called my office landline with what was presented as an extremely urgent assignment.
Our kid’s new homeroom teacher had dropped a last-minute task on her through WeChat. She sent over two lists: class roster A, and software usage record B exported from some school app. The teacher wanted every name that appeared in B but not in A marked with a red background, and every name that appeared in A but not in B reported separately.
In terms a human can actually process, the job was to find （A – A ∩ B） 和（ B – A ∩ B）.
Why this responsibility landed on my wife in the first place remains unclear.
The real problem was that she was off work and out shopping. She had no idea how to handle this on her phone. Her exact complaint was: “The screen can’t show enough at once. I can’t do it.” I assume her plan had been to sort both lists and compare them by eye.
The trouble is, I dislike doing this kind of thing on a phone even more than she does. And at work, I couldn’t use my phone freely anyway.
So the operation began.
First, I ran to the break room and emailed the spreadsheet and compressed file to myself as attachments.
Second, I ran back to my desk, opened the files, edited the sheet, and filled two columns with MATCH formulas to get the answer. I found the entry belonging to （ B – A ∩ B）, highlighted it red as requested, saved the file, and emailed it to myself. Then I noted down the one name in （A – A ∩ B） so I could send it back as a message.
Third, I went back to the break room, downloaded the attachment, and forwarded it to my wife on WeChat.
Fourth, I started typing out the missing name from the other side of the comparison.
That fourth step lasted maybe 30 seconds before my wife called again in full pursuit mode: “Wasn’t there also someone from their class who didn’t show up on the list? Did you forget?”
And there I was, completely unable to defend myself.
The unlucky child’s name included yin—the indium in boron, aluminum, gallium, indium, thallium. Outside of high school chemistry, that character basically never enters normal life. Even in chemistry class, the only thing most people ever remember about indium is probably how its electrons are distributed across shells.
Characters like that create their own kind of distance: familiar enough that you recognize them, rare enough that your eyes slide right past them. The name had actually shown up on page 3, and I somehow skipped over it completely. By the time the phone rang, I had already gone through 11 pages out of 17 under the pronunciation “yin.”
Really, wouldn’t it make more sense to blame the child’s parents—or perhaps whichever fortune-teller helped choose the name?
Still, fine, this one can be pinned on me too.
Who told me to skip the Wubi typing class at that computer course 26 years ago?