https://leanprover-community.github.io/mathlib4_docs/Mathlib/LinearAlgebra/QuadraticForm/AlgClosed.html
Mathlib.LinearAlgebra.QuadraticForm.AlgClosed
mathlib
https://leanprover-community.github.io/mathlib4_docs/Counterexamples/QuadraticForm.html
Counterexamples.QuadraticForm
counterexamples