English
If i and j are such that P.root i + P.root j lies in the range of P.root, then [P.root i, P.root j] are linearly independent.
Русский
Если i и j таковы, что P.root i + P.root j лежит в образе P.root, то векторная пара {P.root i, P.root j} линейно независима.
LaTeX
$$$$ (P.root i + P.root j) \\in \\operatorname{range}(P.root) \\Rightarrow \\operatorname{LI}_R(\\![P.root i, P.root j]\\!). $$$$
Lean4
theorem linearIndependent_iff [Nontrivial R] [P.IsReduced] :
LinearIndependent R ![P.root i, P.root j] ↔ i ≠ j ∧ P.root i ≠ -P.root j :=
by
refine ⟨fun h ↦ ?_, fun ⟨h, h'⟩ ↦ linearIndependent P h h'⟩
rw [LinearIndependent.pair_iff] at h
contrapose! h
rcases eq_or_ne i j with rfl | h'
· exact ⟨1, -1, by simp⟩
· rw [h h']
exact ⟨1, 1, by simp⟩