In this paper, we derive a comparison principle for non-negative weak sub- and super-solutions to doubly nonlinear parabolic partial differential equations whose prototype is $$\begin{aligned} \partial _t u^q - {{\,\textrm{div}\,}}{\big (|\nabla u|^{p-2}\nabla u \big )}=0 \qquad \text{ in } \Omega _T, \end{aligned}$$
∂
t
u
q
-
div
(
|
∇
u
|
p
-
2
∇
u
)
=
0
in
Ω
T
,
with $$q>0$$
q
>
0
and $$p>1$$
p
>
1
and $$\Omega _T:=\Omega \times (0,T)\subset \mathbb {R}^{n+1}$$
Ω
T
:
=
Ω
×
(
0
,
T
)
⊂
R
n
+
1
. Instead of requiring a lower bound for the sub- or super-solutions in the whole domain $$\Omega _T$$
Ω
T
, we only assume the lateral boundary data to be strictly positive. The main results yield some applications. Firstly, we obtain uniqueness of non-negative weak solutions to the associated Cauchy–Dirichlet problem. Secondly, we prove that any weak solution is also a viscosity solution.