* Where they represent pegs as natural numbers, that corresponds to our representing locations in a store by their indexes in the store.
-* Where they say "reference system," which they use the leter `r` for, that corresponds to what we've been calling "assignments", and use the letter `g` for.
+* Where they say "reference system," which they use the leter `r` for, that corresponds to what we've been calling "assignments", and have been using the letter `g` for.
* Where they say `r[x/n]`, that's our `g{x:=n}`.
* Their function `g`, which assigns objects from the domain to pegs, corresponds to our store function, which assigns entities to indexes.
+* At several places they talk about some things being *real extensions* of other things. This confused me at first, because they don't ever define a notion of "real extension." (They do define what they mean by "an extension.") At one point in the paper, it emerges that what they mean is what I'd call a *proper extension*: an extension which isn't identical to the original.
+
* [More hints](/hints/assignment_7_hint_2).