FIX: use correct syntax for ref link

docs/usage/combine.ipynb

@@ -74,7 +74,7 @@
     "tags": []
    },
    "source": [
-    "This notebooks shows how to combine two {class}`.ReactionInfo` objects that describe transitions for one equivalent initial-to-final state reaction. In this example, we have one {class}`.ReactionInfo` object that is generated all selection rules for the strong force and one that is generated for with {ref}`specific interaction types per node <usage/reaction#Select interaction types>`."
+    "This notebooks shows how to combine two {class}`.ReactionInfo` objects that describe transitions for one equivalent initial-to-final state reaction. In this example, we have one {class}`.ReactionInfo` object that is generated all selection rules for the strong force and one that is generated for with {ref}`specific interaction types per node <usage/reaction:Select interaction types>`."
    ]
   },
   {