English
The composition of the self-adjoint part with the skew-adjoint subtype is the identity.
Русский
Состав самосопряжённой части с подтипом космодружённых даёт тождество.
LaTeX
$$$(\text{selfAdjointPart})(\text{skewAdjoint.submodule } R A).subtype = \mathrm{id}$$$
Lean4
@[simp]
theorem skewAdjointPart_comp_subtype_skewAdjoint : (skewAdjointPart R).comp (skewAdjoint.submodule R A).subtype = .id :=
LinearMap.ext fun ⟨x, (hx : _ = _)⟩ ↦
Subtype.eq <| by
simp only [LinearMap.comp_apply, Submodule.subtype_apply, skewAdjointPart_apply_coe, hx, sub_neg_eq_add, smul_add,
invOf_two_smul_add_invOf_two_smul];
rfl