English
Every scalar from R acting on ℂ via Real scalars is central: r z = z r for all r ∈ R, z ∈ ℂ.
Русский
Каждый скаляр из R, действующий на ℂ через вещественные скаляры, центральен: r z = z r.
LaTeX
$$$\\\\forall r \\\\in R, \\\\forall z \\\\in \\\\mathbb{C}, r \\\\cdot z = z \\\\cdot r$$$
Lean4
instance (priority := 90) [SMul R S] [SMul R ℝ] [SMul S ℝ] [IsScalarTower R S ℝ] : IsScalarTower R S ℂ where
smul_assoc r s
x := by
ext <;>
simp [smul_re, smul_im, smul_assoc]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980