I’m not acquainted with NF, but to my perspective what the comment I was replying to was suggesting is that the structures can’t express anything about a struct

I’m not acquainted with NF, but to my perspective what the comment I was replying to was suggesting is that the structures can’t express anything about a structure of the same level of comprehension. Which, to my mind, implies that an expression should not be allowed to embed an expression. Which is roughly equivalent to disallow a code to embed code written in the same language, let alone a code aware of the language structure and able manipulate the current code base abstract syntax tree or any equivalent facility. Once again, I don’t claim this about NF, which I wasn’t aware of before this thread. I never dug into Quine’s work to be transparent on the matter.