diff --git a/src/torchjd/aggregation/_aligned_mtl.py b/src/torchjd/aggregation/_aligned_mtl.py
index f0e62860..eadef9ab 100644
--- a/src/torchjd/aggregation/_aligned_mtl.py
+++ b/src/torchjd/aggregation/_aligned_mtl.py
@@ -25,7 +25,7 @@
 # SOFTWARE.
 
 
-from typing import Literal
+from typing import Literal, TypeAlias
 
 import torch
 from torch import Tensor
@@ -37,6 +37,8 @@
 from ._utils.pref_vector import pref_vector_to_str_suffix, pref_vector_to_weighting
 from ._weighting_bases import Weighting
 
+SUPPORTED_SCALE_MODE: TypeAlias = Literal["min", "median", "rmse"]
+
 
 class AlignedMTL(GramianWeightedAggregator):
     r"""
@@ -58,10 +60,10 @@ class AlignedMTL(GramianWeightedAggregator):
     def __init__(
         self,
         pref_vector: Tensor | None = None,
-        scale_mode: Literal["min", "median", "rmse"] = "min",
+        scale_mode: SUPPORTED_SCALE_MODE = "min",
     ):
         self._pref_vector = pref_vector
-        self._scale_mode = scale_mode
+        self._scale_mode: SUPPORTED_SCALE_MODE = scale_mode
         super().__init__(AlignedMTLWeighting(pref_vector, scale_mode=scale_mode))
 
     def __repr__(self) -> str:
@@ -89,11 +91,11 @@ class AlignedMTLWeighting(Weighting[PSDMatrix]):
     def __init__(
         self,
         pref_vector: Tensor | None = None,
-        scale_mode: Literal["min", "median", "rmse"] = "min",
+        scale_mode: SUPPORTED_SCALE_MODE = "min",
     ):
         super().__init__()
         self._pref_vector = pref_vector
-        self._scale_mode = scale_mode
+        self._scale_mode: SUPPORTED_SCALE_MODE = scale_mode
         self.weighting = pref_vector_to_weighting(pref_vector, default=MeanWeighting())
 
     def forward(self, gramian: PSDMatrix) -> Tensor:
@@ -105,7 +107,7 @@ def forward(self, gramian: PSDMatrix) -> Tensor:
 
     @staticmethod
     def _compute_balance_transformation(
-        M: Tensor, scale_mode: Literal["min", "median", "rmse"] = "min"
+        M: Tensor, scale_mode: SUPPORTED_SCALE_MODE = "min"
     ) -> Tensor:
         lambda_, V = torch.linalg.eigh(M, UPLO="U")  # More modern equivalent to torch.symeig
         tol = torch.max(lambda_) * len(M) * torch.finfo().eps
diff --git a/src/torchjd/aggregation/_dualproj.py b/src/torchjd/aggregation/_dualproj.py
index 202f204a..d91e32aa 100644
--- a/src/torchjd/aggregation/_dualproj.py
+++ b/src/torchjd/aggregation/_dualproj.py
@@ -1,12 +1,10 @@
-from typing import Literal
-
 from torch import Tensor
 
 from torchjd._linalg import PSDMatrix, normalize, regularize
 
 from ._aggregator_bases import GramianWeightedAggregator
 from ._mean import MeanWeighting
-from ._utils.dual_cone import project_weights
+from ._utils.dual_cone import SUPPORTED_SOLVER, project_weights
 from ._utils.non_differentiable import raise_non_differentiable_error
 from ._utils.pref_vector import pref_vector_to_str_suffix, pref_vector_to_weighting
 from ._weighting_bases import Weighting
@@ -34,12 +32,12 @@ def __init__(
         pref_vector: Tensor | None = None,
         norm_eps: float = 0.0001,
         reg_eps: float = 0.0001,
-        solver: Literal["quadprog"] = "quadprog",
+        solver: SUPPORTED_SOLVER = "quadprog",
     ):
         self._pref_vector = pref_vector
         self._norm_eps = norm_eps
         self._reg_eps = reg_eps
-        self._solver = solver
+        self._solver: SUPPORTED_SOLVER = solver
 
         super().__init__(
             DualProjWeighting(pref_vector, norm_eps=norm_eps, reg_eps=reg_eps, solver=solver)
@@ -78,14 +76,14 @@ def __init__(
         pref_vector: Tensor | None = None,
         norm_eps: float = 0.0001,
         reg_eps: float = 0.0001,
-        solver: Literal["quadprog"] = "quadprog",
+        solver: SUPPORTED_SOLVER = "quadprog",
     ):
         super().__init__()
         self._pref_vector = pref_vector
         self.weighting = pref_vector_to_weighting(pref_vector, default=MeanWeighting())
         self.norm_eps = norm_eps
         self.reg_eps = reg_eps
-        self.solver = solver
+        self.solver: SUPPORTED_SOLVER = solver
 
     def forward(self, gramian: PSDMatrix) -> Tensor:
         u = self.weighting(gramian)
diff --git a/src/torchjd/aggregation/_upgrad.py b/src/torchjd/aggregation/_upgrad.py
index c7efb367..132b72e6 100644
--- a/src/torchjd/aggregation/_upgrad.py
+++ b/src/torchjd/aggregation/_upgrad.py
@@ -1,5 +1,3 @@
-from typing import Literal
-
 import torch
 from torch import Tensor
 
@@ -7,7 +5,7 @@
 
 from ._aggregator_bases import GramianWeightedAggregator
 from ._mean import MeanWeighting
-from ._utils.dual_cone import project_weights
+from ._utils.dual_cone import SUPPORTED_SOLVER, project_weights
 from ._utils.non_differentiable import raise_non_differentiable_error
 from ._utils.pref_vector import pref_vector_to_str_suffix, pref_vector_to_weighting
 from ._weighting_bases import Weighting
@@ -35,12 +33,12 @@ def __init__(
         pref_vector: Tensor | None = None,
         norm_eps: float = 0.0001,
         reg_eps: float = 0.0001,
-        solver: Literal["quadprog"] = "quadprog",
+        solver: SUPPORTED_SOLVER = "quadprog",
     ):
         self._pref_vector = pref_vector
         self._norm_eps = norm_eps
         self._reg_eps = reg_eps
-        self._solver = solver
+        self._solver: SUPPORTED_SOLVER = solver
 
         super().__init__(
             UPGradWeighting(pref_vector, norm_eps=norm_eps, reg_eps=reg_eps, solver=solver)
@@ -79,14 +77,14 @@ def __init__(
         pref_vector: Tensor | None = None,
         norm_eps: float = 0.0001,
         reg_eps: float = 0.0001,
-        solver: Literal["quadprog"] = "quadprog",
+        solver: SUPPORTED_SOLVER = "quadprog",
     ):
         super().__init__()
         self._pref_vector = pref_vector
         self.weighting = pref_vector_to_weighting(pref_vector, default=MeanWeighting())
         self.norm_eps = norm_eps
         self.reg_eps = reg_eps
-        self.solver = solver
+        self.solver: SUPPORTED_SOLVER = solver
 
     def forward(self, gramian: PSDMatrix) -> Tensor:
         U = torch.diag(self.weighting(gramian))
diff --git a/src/torchjd/aggregation/_utils/dual_cone.py b/src/torchjd/aggregation/_utils/dual_cone.py
index 539685be..b076366b 100644
--- a/src/torchjd/aggregation/_utils/dual_cone.py
+++ b/src/torchjd/aggregation/_utils/dual_cone.py
@@ -1,12 +1,14 @@
-from typing import Literal
+from typing import Literal, TypeAlias
 
 import numpy as np
 import torch
 from qpsolvers import solve_qp
 from torch import Tensor
 
+SUPPORTED_SOLVER: TypeAlias = Literal["quadprog"]
 
-def project_weights(U: Tensor, G: Tensor, solver: Literal["quadprog"]) -> Tensor:
+
+def project_weights(U: Tensor, G: Tensor, solver: SUPPORTED_SOLVER) -> Tensor:
     """
     Computes the tensor of weights corresponding to the projection of the vectors in `U` onto the
     rows of a matrix whose Gramian is provided.
@@ -25,7 +27,7 @@ def project_weights(U: Tensor, G: Tensor, solver: Literal["quadprog"]) -> Tensor
     return torch.as_tensor(W, device=G.device, dtype=G.dtype)
 
 
-def _project_weight_vector(u: np.ndarray, G: np.ndarray, solver: Literal["quadprog"]) -> np.ndarray:
+def _project_weight_vector(u: np.ndarray, G: np.ndarray, solver: SUPPORTED_SOLVER) -> np.ndarray:
     r"""
     Computes the weights `w` of the projection of `J^T u` onto the dual cone of the rows of `J`,
     given `G = J J^T` and `u`. In other words, this computes the `w` that satisfies