English
For a quadratic form Q1, composing with the right id-tensor yields the same as tensoring with the square map: Q1 ∘ (rid) = Q1 ⊗ sq.
Русский
Для квадратичной формы Q1 композиция с правым тензорным единичным отображением rid равна Q1 ⊗ sq.
LaTeX
$$$Q_1 \circ (\mathrm{TensorProduct}.rid\,R\,M_1) = Q_1 \otimes \mathrm{sq}(R := R).$$$
Lean4
theorem comp_tensorRId_eq (Q₁ : QuadraticForm R M₁) : Q₁.comp (TensorProduct.rid R M₁) = Q₁.tmul (sq (R := R)) :=
by
refine (QuadraticMap.associated_rightInverse R).injective ?_
ext m₁ m₁'
dsimp [-associated_apply]
simp only [associated_tmul, QuadraticMap.associated_comp]
simp [-associated_apply, one_mul]