From: Jim Pryor Date: Thu, 18 Nov 2010 22:50:04 +0000 (-0500) Subject: assignment7 tweaks X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=641e2e0035a5e3225f719c0ef201f93362b0f8ad;hp=157b0b898f07c15b13e42718fab380c4ee69d7ea assignment7 tweaks Signed-off-by: Jim Pryor --- diff --git a/hints/assignment_7_hint_3.mdwn b/hints/assignment_7_hint_3.mdwn index 4a159e9e..61f48a71 100644 --- a/hints/assignment_7_hint_3.mdwn +++ b/hints/assignment_7_hint_3.mdwn @@ -27,9 +27,9 @@ More specifically, \[[expression]] will be a set of `'a discourse_possibility` m (* the reason for returning a triple with () in first position will emerge *) in ((), r',g') -* At the top of p. 13 (this is in between defs 2.8 and 2.9), GS&V give two examples, one for \[[∃xPx]] and the other for \[[Qx]]. In fact it will be easiest for us to break \[[∃xPx]] into two pieces, \[[∃x]] and \[[Px]]. Let's consider expressions like \[[Px]] (or \[[Qx]]) first. +* At the top of p. 13 (this is in between defs 2.8 and 2.9), GS&V give two examples, one for \[[∃xPx]] and the other for \[[Qx]]. In fact it will be easiest for us to break \[[∃xPx]] into two pieces, \[[∃x]] and \[[Px]]. Let's consider expressions like \[[Px]] first. - They say that the effect of updating an information state `s` with the formula `Qx` should be to eliminate possibilities in which the object associated with the peg associated with the variable `x` does not have the property Q. In other words, if we let `Q` be a function from objects to `bool`s, `s` updated with \[[Qx]] should be `s` filtered by the function `fun (r, g) -> let obj = List.nth g (r 'x') in Q obj`. + They say that the effect of updating an information state `s` with the meaning of "Qx" should be to eliminate possibilities in which the object associated with the peg associated with the variable `x` does not have the property Q. In other words, if we let `Q` be a function from objects to `bool`s, `s` updated with \[[Qx]] should be `s` filtered by the function `fun (r, g) -> let obj = List.nth g (r 'x') in Q obj`. Recall that [we said before](/hints/assignment_7_hint_2) that `List.filter (test : 'a -> bool) (u : 'a set) : 'a set` is the same as: