diff --git a/SC2039.md b/SC2039.md
index 82bcbfa..cbde9c2 100644
--- a/SC2039.md
+++ b/SC2039.md
@@ -70,8 +70,8 @@ Bash:
 POSIX:
 
 ```sh
-: $((a=c+d))
-[ $((d)) -ne 0 ] && echo d is true.
+: $((a=c+d)) # discard the output of the arith expn with `:` command
+[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
 ```
 
 ### `select` loops