No, that doesn't make sense to me. The inverse of & would be a computable function that takes the Gödel number of a unary numeral and returns the number represented by that numeral. #[...] is syntactic sugar somewhat similar to the $NAME in e.g. Perl's "Hello, $NAME!".

But "#[&7]" = "7", and if you replace the 7s with some other number, it's still true, right?

"n >= 7" would mean an expression that contains the variable n, rather than an expression containing the unary numeral representing the numeric value of n.

Got it.

No, wait, that's completely wrong. We need to distinguish between applying repr(.) to an argument and constructing the Gödel number of an expression in which repr(.) is applied to an argument. For example, in my earlier comment, plus(x,y) was not equal to (x+y): if x and y are the Gödel numbers of two expressions, then (x+y) would simply add those Gödel numbers (which isn't useful), whereas plus(x,y) returns the Gödel number of an expression (namely the expression adding the expressions denoted by the Gödel numbers x and y). Do you see what I mean?

Oh, I see. Everything after that paragraph, I'm going to have to think about for a while. Edit: got it (I think).