diff --git a/doc/index.md b/doc/index.md
new file mode 100644
index 0000000..da40b8c
--- /dev/null
+++ b/doc/index.md
@@ -0,0 +1,38 @@
+# Documentation
+
+## prevent last false
+
+function body should not end up with a ternary statement
+
+### wrong last
+
+Compound of 2 'false' statement returns false.
+
+```bash
+[[ : ]] && [[ : ]]
+```
+
+### right last
+
+```bash
+[[ : ]] && [[ : ]] || true
+```
+
+## arithmetic issue
+
+last (++) statement does not complete successfully!
+
+### wrong ++
+
+```bash
+count=0
+(( ++count )) # ok 
+(( ++count )) # last statement in function returns false
+```
+
+### right ++
+
+```bash
+count=0
+count=$((count+1))
+```