Update some snippets

snippets/difference.md

@@ -1,16 +1,18 @@
 ---
 title: difference
-tags: list
+tags: list,beginner
 ---
+
 Returns the difference between two iterables.
 
-Use list comprehension to only keep values not contained in `b`.
+Create a `set` fromn `b`, then use list comprehension on `a` to only keep values not contained in the previously created set, `_b`.
 
 ```py
 def difference(a, b):
-    _b = set(b)
-    return [item for item in a if item not in _b]
+  _b = set(b)
+  return [item for item in a if item not in _b]
 ```
+
 ```py
 difference([1, 2, 3], [1, 2, 4]) # [3]
 ```