From: Jim Pryor <profjim@jimpryor.net>
Date: Thu, 16 Sep 2010 01:29:17 +0000 (-0400)
Subject: week1: tweaks
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=d00df5e3fde439b66a7d6b712d2b6b09cf9d763a

week1: tweaks

Signed-off-by: Jim Pryor <profjim@jimpryor.net>
---

diff --git a/week1.mdwn b/week1.mdwn
index 5d482c4c..20f33b32 100644
--- a/week1.mdwn
+++ b/week1.mdwn
@@ -56,7 +56,18 @@ It's possible to enhance the lambda calculus so that functions do get identified
 
 It's often said that dynamic systems are distinguished because they are the ones in which **order matters**. However, there are many ways in which order can matter. If we have a trivalent boolean system, for example---easily had in a purely functional calculus---we might choose to give a truth-table like this for "and":
 
-	true and true   = true
+<pre><code>
+true and true   = true
+true and true   = true
+true and *      = *
+true and false  = false
+* and true      = *
+* and *         = *
+* and false     = *
+false and true  = false
+false and *     = false
+false and false = false
+</code></pre>
 
 And then we'd notice that `* and false` has a different intepretation than `false and *`. (The same phenomenon is already present with the material conditional in bivalent logics; but seeing that a non-symmetric semantics for `and` is available even for functional languages is instructive.)