{"ast_node_type":"other","tokens":[{"end":78,"kind":"keyword","start":0,"text":"(FlatSet::Elem(const_arg),"}]}
            (FlatSet::Elem(const_arg), _) | (_, FlatSet::Elem(const_arg)) => {
            // Exactly one side is known, attempt some algebraic simplifications.
                let layout = const_arg.layout;