Let G(D) be a linear partial differential operator on $${\mathbb {R}}^n$$
R
n
, with constant coefficients. Moreover let $$\Omega \subset {\mathbb {R}}^n$$
Ω
⊂
R
n
be open and $$F\in L^1_{\text {loc}} (\Omega , {\mathbb {C}}^N)$$
F
∈
L
loc
1
(
Ω
,
C
N
)
. Then any set of the form $$\begin{aligned} A_{f,F}:= \{ x\in \Omega \, \vert \, (G(D)f)(x)=F(x)\}, \text { with }f\in W^{g,1}_{\text {loc}}(\Omega , {\mathbb {C}}^k) \end{aligned}$$
A
f
,
F
:
=
{
x
∈
Ω
|
(
G
(
D
)
f
)
(
x
)
=
F
(
x
)
}
,
with
f
∈
W
loc
g
,
1
(
Ω
,
C
k
)
is said to be a G-primitivity domain of F. We provide some results about the structure of G-primitivity domains of F at the points of the (suitably defined) G-nonintegrability set of F. A Lusin type theorem for G(D) is also provided. Finally, we give applications to the Maxwell type system and to the multivariate Cauchy-Riemann system.