English
For χ and ψ, the primitive multiplication is given by the primitive character of the product: χ.primitive_mul ψ = primitiveCharacter (mul χ ψ).
Русский
Для χ и ψ примитивное произведение задаётся как примитивный символ от произведения: χ.primitive_mul ψ = primitiveCharacter (mul χ ψ).
LaTeX
$$$\\chi.primitive\\_mul \\psi = \\mathrm{primitiveCharacter}(\\chi \\mul \\psi).$$$
Lean4
theorem mul_def {n m : ℕ} {χ : DirichletCharacter R n} {ψ : DirichletCharacter R m} :
χ.primitive_mul ψ = primitiveCharacter (mul χ ψ) :=
rfl