Created SC1106 (markdown)

SC1106.md

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+## In arithmetic contexts, use `<` instead of `-lt`
+
+Similarly, `>` instead of `-gt`, `<=` instead of `-le`, `>=` instead of `-ge`, `==` instead of `-eq`, `!=` instead of `-ne`.
+
+### Problematic code:
+
+```sh
+if (( 2 -lt 3 ))
+then
+  echo "True"
+fi
+```
+
+### Correct code:
+
+```sh
+if (( 2 < 3 ))
+then
+  echo "True"
+fi
+```
+
+### Rationale:
+
+The comparators `-lt`, `-ge`, `-eq` and friends are flags for the `test` command aka `[`. You are instead using it in an arithmetic context, such as `(( .. ))` or `$(( .. ))`, where you should be using `<`, `>=`, `==` etc instead. 
+
+In arithmetic contexts, `-lt` is simply interpreted as "subtract the value of `$lt`", which is clearly not the intention.
+ 
+### Exceptions:
+
+If you do want to subtract `$lt` you can add a space to make this clear to ShellCheck: `echo $((3 - lt))`
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!