alue_type,
                                                                                           typename E2::value_type&gt;::promote_type&gt; &gt;::result_type
    inner_prod (const vector_expression&lt;E1&gt; &amp;e1,
                const vector_expression&lt;E2&gt; &amp;e2);

    template&lt;class E1, class E2&gt;
    typename vector_scalar_binary_traits&lt;E1, E2, vector_inner_prod&lt;typename E1::value_type,
                                                                   typename E2::value_typ