The curl of an order- n > 1 tensor field T ( x ) is also defined using the recursive relation ( ∇ ∇ × × T ) ⋅ ⋅ c = ∇ ∇ × × ( c ⋅ ⋅ T ) ; ( ∇ ∇ × × v ) ⋅ ⋅ c = ∇ ∇ ⋅ ⋅ ( v × × c ) where c is an arbitrary constant vector and v is a vector field.