Let
$F(x_1, x_2, x_3) = F_1(x_1, x_2, x_3) i + F_2(x_1, x_2, x_3)j + F_3(x_1, x_2, x_3)k$
be a vector field. If $F_i$ is not a a function of $x_i$ for all $i$, then $F$ is incompressible. If $F_i$ is only a function of $x_i$ for all $i$, then $F$ is irrotational. However, we can only apply one of these tests at a time.
Are there any "quick" (no computation or plotting allowed) techniques for telling when a vector field must be BOTH irrotational and incompressible?