fixes #836 (#1023)

Author: martin-henz

xml/chapter3/section3/subsection4.xml

@@ -570,21 +570,6 @@ function logical_and(s1, s2) {
 }
     </JAVASCRIPT>
   </SNIPPET>
-  <SNIPPET HIDE="yes">
-    <NAME>logical_or</NAME>
-    <JAVASCRIPT>
-function logical_or(s1, s2) {
-    return s1 === 0 &amp;&amp; s2 === 0
-           ? 0
-           : s1 === 0 || s1 === 1
-           ? s2 === 0 || s2 === 1
-             ? 1
-             : error(s2, "invalid signal")
-           : error(s1, "invalid signal");
-}
-    </JAVASCRIPT>
-  </SNIPPET>
-  
   <PDF_ONLY>
     <!-- Figure moved here from earlier for SICP JS pagination -->
     <!-- Figure code is copy of code earlier in this file in a WEB_ONLY -->
@@ -673,12 +658,32 @@ function and_gate(a1, a2, output) {
       <JAVASCRIPT><JAVASCRIPTINLINE>and_gate</JAVASCRIPTINLINE>.
       </JAVASCRIPT>
     </SPLITINLINE>
-    <SNIPPET HIDE="yes">
-      <NAME>or_gate</NAME>
-      <REQUIRES>get_signal</REQUIRES>
-      <REQUIRES>after_delay</REQUIRES>
-      <REQUIRES>logical_or</REQUIRES>
-      <JAVASCRIPT>
+    <LABEL NAME="ex:3_28"/>
+    <SOLUTION>
+      <SNIPPET>
+	<NAME>logical_or</NAME>
+	<JAVASCRIPT>
+// contributed by GitHub user clean99
+
+function logical_or(s1, s2) {
+    return s1 === 0 &amp;&amp; s2 === 0
+           ? 0
+           : s1 === 0 || s1 === 1
+           ? s2 === 0 || s2 === 1
+             ? 1
+             : error(s2, "invalid signal")
+           : error(s1, "invalid signal");
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+      <SNIPPET>
+	<NAME>or_gate</NAME>
+	<REQUIRES>get_signal</REQUIRES>
+	<REQUIRES>after_delay</REQUIRES>
+	<REQUIRES>logical_or</REQUIRES>
+	<JAVASCRIPT>
+// contributed by GitHub user clean99
+
 function or_gate(a1, a2, output) {
     function or_action_function() {
         const new_value = logical_or(get_signal(a1),
@@ -690,9 +695,9 @@ function or_gate(a1, a2, output) {
     add_action(a2, or_action_function);
     return "ok";
 }
-      </JAVASCRIPT>
-    </SNIPPET>
-    <LABEL NAME="ex:3_28"/>
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>