∀ {K : Type u_2} {L : Type u_3} [inst : LieRing L] [inst_1 : Field K] [inst_2 : LieAlgebra K L] [FiniteDimensional K L]
  {H : LieSubalgebra K L} [inst_4 : H.IsCartanSubalgebra] [LieAlgebra.IsKilling K L]
  [LieModule.IsTriangularizable K (↥H) L] [CharZero K] (α : LieModule.Weight K (↥H) L),
  α.IsNonZero → Module.finrank K ↥(LieAlgebra.rootSpace H ⇑α) = 1