For a second-order tensor S c ⋅ ⋅ S = c m S m j e j Hence, using the definition of the curl of a first-order tensor field, ∇ ∇ × × ( c ⋅ ⋅ S ) = ε ε i j k c m S m j , i e k = ( ε ε i j k S m j , i e k ⊗ ⊗ e m ) ⋅ ⋅ c = ( ∇ ∇ × × S ) ⋅ ⋅ c Therefore, we have ∇ ∇ × × S = ε ε i j k S m j , i e k ⊗ ⊗ e m