Can the same variable not appear twice in a literal?

[JeffreyBenjaminBrown]

I ask because the README says "Rewrite literals like f(X,X) into f(X,Y), X=Y. A few internals assume that the same variable doesn't appear twice in a literal" -- but it says that under "Planned Enhancements", as opposed to (a hypothetical section called) "instructions to the user".

[travitch]

It has been a very long time since I looked at this library, but that sounds like something that could be true. I don't have any idea off the top of my head why it ended up that way.