22 Dg_Expr<minus_Dg<A, T, Dim01, Dim2, i, j, k>,
T, Dim01, Dim2,
i,
j,
k>
Ddg_Expr< Ddg_minus_Ddg< A, B, T, U, Dim01, Dim23, i, j, k, l >, typename promote< T, U >::V, Dim01, Dim23, i, j, k, l > operator-(const Ddg_Expr< A, T, Dim01, Dim23, i, j, k, l > &a, const Ddg_Expr< B, U, Dim01, Dim23, i, j, k, l > &b)