X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=hints%2Fassignment_7_hint_1.mdwn;h=6d6b760b21baf7e745dd53c23185a118cd5592aa;hp=f7d5d288fc4a0fe7f9dcb79519cad2b703a59da9;hb=2dd3d25af2cc061385f8544bd7137f4f869d3d98;hpb=4e38540a3d46c09c41f6c4591ab9b39b401ce050 diff --git a/hints/assignment_7_hint_1.mdwn b/hints/assignment_7_hint_1.mdwn index f7d5d288..6d6b760b 100644 --- a/hints/assignment_7_hint_1.mdwn +++ b/hints/assignment_7_hint_1.mdwn @@ -3,11 +3,13 @@ * 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}`. +* Where they say `r[x/n]`, that's our `g{x:=n}`, or in OCaml, `fun v -> if v = 'x' then n else g v`. -* Their function `g`, which assigns objects from the domain to pegs, corresponds to our store function, which assigns entities to indexes. +* Their function `g`, which assigns objects from the domain to pegs, corresponds to our store function, which assigns entities to indexes. To avoid confusion, I'll use `r` for assignments, like they do, and avoid using `g` altogether. Instead I'll use `h` for stores. (We can't use `s` because GS&V use that for something else, which they call "information states.") + +* 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 "extensions.") 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).