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diff --git a/week4.mdwn b/week4.mdwn
index e69832fd..5e219484 100644
--- a/week4.mdwn
+++ b/week4.mdwn
@@ -6,11 +6,11 @@ A: That's easy: let `T` be an arbitrary term in the lambda calculus.  If
 `T` has a fixed point, then there exists some `X` such that `X <~~>
 TX` (that's what it means to *have* a fixed point).
 
-<pre>
-let W = \x.T(xx) in
-let X = WW in
-X = WW = (\x.T(xx))W = T(WW) = TX
-</pre>
+<pre><code>
+let L = \x. T (x x) in
+let X = L L in
+X &equiv; L L &equiv; (\x. T (x x)) L ~~> T (L L) &equiv; T X
+</code></pre>
 
 Please slow down and make sure that you understand what justified each
 of the equalities in the last line.