From 1e4eb8b9602d21fc6d40d96b6072fff151b8b5b7 Mon Sep 17 00:00:00 2001
From: henz <henz@comp.nus.edu.sg>
Date: Sun, 30 Jun 2024 19:33:11 +0800
Subject: [PATCH 1/2] fixes #807

---
 xml/chapter2/section5/subsection3.xml | 31 +++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/xml/chapter2/section5/subsection3.xml b/xml/chapter2/section5/subsection3.xml
index 3971aca7e..a30a2af78 100644
--- a/xml/chapter2/section5/subsection3.xml
+++ b/xml/chapter2/section5/subsection3.xml
@@ -1025,6 +1025,37 @@ head(tail(tail(tail(mul(p1, p2)))));
     subtraction of polynomials.
     (Hint: You may find it helpful to define a generic negation operation.)
     <LABEL NAME="ex:sub-poly"/>
+    <SOLUTION>
+      <SNIPPET>
+	<NAME>ex_2_88_solution</NAME>
+	<JAVASCRIPT>
+function sub_terms(L1, L2) {
+    if (is_empty_termlist(L1)) {
+        return L2;
+    } else if (is_empty_termlist(L2)) {
+        return L1;
+    } else {
+        const t1 = first_term(L1);
+        const t2 = first_term(L2);
+        return order(t1) &gt; order(t2)
+               ? adjoin_term(t1, sub_terms(rest_terms(L1), L2))
+               : order(t1) &lt; order(t2)
+               ? adjoin_term(t2, sub_terms(L1, rest_terms(L2)))
+               : adjoin_term(make_term(order(t1), 
+                                       sub(coeff(t1), coeff(t2))),
+                             sub_terms(rest_terms(L1),
+                                       rest_terms(L2)));
+    }
+}
+function sub_poly(p1, p2) {
+    return is_same_variable(variable(p1), variable(p2))
+           ? make_poly(variable(p1),
+                       sub_terms(term_list(p1), term_list(p2)))
+           : error(list(p1, p2), "polys not in same var -- sub_poly");
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>

From 7b358adae808d72bf3828d91b56876441196adca Mon Sep 17 00:00:00 2001
From: henz <henz@comp.nus.edu.sg>
Date: Sun, 30 Jun 2024 19:52:02 +0800
Subject: [PATCH 2/2] no eval here

---
 xml/chapter2/section5/subsection3.xml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xml/chapter2/section5/subsection3.xml b/xml/chapter2/section5/subsection3.xml
index a30a2af78..8f76c839e 100644
--- a/xml/chapter2/section5/subsection3.xml
+++ b/xml/chapter2/section5/subsection3.xml
@@ -1026,7 +1026,7 @@ head(tail(tail(tail(mul(p1, p2)))));
     (Hint: You may find it helpful to define a generic negation operation.)
     <LABEL NAME="ex:sub-poly"/>
     <SOLUTION>
-      <SNIPPET>
+      <SNIPPET EVAL="no">
 	<NAME>ex_2_88_solution</NAME>
 	<JAVASCRIPT>
 function sub_terms(L1, L2) {