diff --git a/xml/chapter2/section5/subsection1.xml b/xml/chapter2/section5/subsection1.xml
index 8f3e4192d..98989015d 100644
--- a/xml/chapter2/section5/subsection1.xml
+++ b/xml/chapter2/section5/subsection1.xml
@@ -994,6 +994,54 @@ function install_complex_package() {
arithmetic package. This operation should work for ordinary numbers,
rational numbers, and complex numbers.
+
+
+
+// provided by GitHub user clean99
+
+function is_equal_to_zero(x) {
+ return apply_generic("is_equal", list(x));
+}
+
+function install_javascript_number_package() {
+ // ...
+
+ put("is_equal_to_zero", "javascript_number",
+ x => x === 0);
+
+ // ...
+}
+
+function install_rational_package() {
+ // ...
+
+ function is_equal_to_zero(x) {
+ return numer(x) === 0;
+ }
+
+ put("is_equal_to_zero", "rational",
+ is_equal_to_zero);
+
+ // ...
+}
+
+function install_complex_package() {
+ // ...
+
+ function is_equal_to_zero(z) {
+ return real_part(z) === 0
+ ? imag_part(z) === 0
+ : false;
+ }
+
+ put("is_equal_to_zero", "complex",
+ is_equal_to_zero);
+
+ //...
+}
+
+
+
generic arithmetic operations