Theorem: Orientation.map_eq_neg_iff_det_neg
File: Mathlib/LinearAlgebra/Orientation.lean

tactic: cases isEmpty_or_nonempty ι
state_before: R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
⊢ ↑(map ι f) x = -x ↔ ↑LinearMap.det ↑f < 0

tactic: have H : 0 < finrank R M := by
  rw [← h]
  exact Fintype.card_pos
state_before: case inr
R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : Nonempty ι
⊢ ↑(map ι f) x = -x ↔ ↑LinearMap.det ↑f < 0

tactic: haveI : FiniteDimensional R M := finiteDimensional_of_finrank H
state_before: case inr
R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : Nonempty ι
H : 0 < finrank R M
⊢ ↑(map ι f) x = -x ↔ ↑LinearMap.det ↑f < 0

tactic: rw [map_eq_det_inv_smul _ _ h, units_inv_smul, units_smul_eq_neg_iff, LinearEquiv.coe_det]
state_before: case inr
R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : Nonempty ι
H : 0 < finrank R M
this : FiniteDimensional R M
⊢ ↑(map ι f) x = -x ↔ ↑LinearMap.det ↑f < 0

tactic: have H : finrank R M = 0 := by
  refine' h.symm.trans _
  convert @Fintype.card_of_isEmpty ι _
state_before: case inl
R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : IsEmpty ι
⊢ ↑(map ι f) x = -x ↔ ↑LinearMap.det ↑f < 0

tactic: simp [LinearMap.det_eq_one_of_finrank_eq_zero H, Module.Ray.ne_neg_self x]
state_before: case inl
R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : IsEmpty ι
H : finrank R M = 0
⊢ ↑(map ι f) x = -x ↔ ↑LinearMap.det ↑f < 0

tactic: refine' h.symm.trans _
state_before: R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : IsEmpty ι
⊢ finrank R M = 0

tactic: convert @Fintype.card_of_isEmpty ι _
state_before: R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : IsEmpty ι
⊢ Fintype.card ι = 0

tactic: rw [← h]
state_before: R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : Nonempty ι
⊢ 0 < finrank R M

tactic: exact Fintype.card_pos
state_before: R : Type u_1
inst✝³ : LinearOrderedField R
M : Type u_2
inst✝² : AddCommGroup M
inst✝¹ : Module R M
ι : Type u_3
inst✝ : Fintype ι
_i : FiniteDimensional R M
x : Orientation R M ι
f : M ≃ₗ[R] M
h : Fintype.card ι = finrank R M
h✝ : Nonempty ι
⊢ 0 < Fintype.card ι