English
Two LieSubalgebras are equal iff they have the same membership relation for every element of L.
Русский
Две подалгебры равны тогда, когда для каждого элемента x ∈ L верно x ∈ L' ⇔ x ∈ L''.
LaTeX
$$$$\forall {R} {L} [\text{CommRing } R] [\text{LieRing } L] [\text{LieAlgebra } R L]\ (L' L'' : \text{LieSubalgebra } R L),\ (\forall x, x \in L' \iff x \in L'') \Rightarrow L' = L''. $$$$
Lean4
theorem toSubmodule_injective : Function.Injective ((↑) : LieSubalgebra R L → Submodule R L) := fun L₁' L₂' h ↦
by
rw [SetLike.ext'_iff] at h
rw [← coe_set_eq]
exact h