-- Mathlib/LinearAlgebra/AffineSpace/Independent.lean
theorem affineIndependent_iff_indicator_eq_of_affineCombination_eq (p : ι → P) :
    AffineIndependent k p ↔
      ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
        ∑ i ∈ s1, w1 i = 1 →
          ∑ i ∈ s2, w2 i = 1 →
            s1.affineCombination k p w1 = s2.affineCombination k p w2 →
              Set.indicator (↑s1) w1 = Set.indicator (↑s2) w2

Proof state:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
hw1s : (affineCombination k s p) w1 = p i0
w2 : ι → k := w + w1
hw2 : ∑ i ∈ s, w2 i = 1
⊢ w i0 = 0

Tactic:
have hw2s : s.affineCombination k p w2 = p i0 := by
  simp_all only [w2, ← Finset.weightedVSub_vadd_affineCombination, zero_vadd]

Result:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
hw1s : (affineCombination k s p) w1 = p i0
w2 : ι → k := w + w1
hw2 : ∑ i ∈ s, w2 i = 1
hw2s : (affineCombination k s p) w2 = p i0
⊢ w i0 = 0

Proof state:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
hw1s : (affineCombination k s p) w1 = p i0
w2 : ι → k := w + w1
⊢ w i0 = 0

Tactic:
have hw2 : ∑ i ∈ s, w2 i = 1 := by
  simp_all only [w2, Pi.add_apply, Finset.sum_add_distrib, zero_add]

Result:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
hw1s : (affineCombination k s p) w1 = p i0
w2 : ι → k := w + w1
hw2 : ∑ i ∈ s, w2 i = 1
⊢ w i0 = 0

Proof state:
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha : AffineIndependent k p
s1 s2 : Finset ι
w1 w2 : ι → k
hw1 : ∑ i ∈ s1, w1 i = 1
hw2 : ∑ i ∈ s2, w2 i = 1
heq : (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2
i : ι
hi : i ∉ ↑s1 ∪ ↑s2
⊢ (↑s1).indicator w1 i = 0

Tactic:
simp only [Set.indicator, Finset.mem_coe, ite_eq_right_iff]

Result:
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha : AffineIndependent k p
s1 s2 : Finset ι
w1 w2 : ι → k
hw1 : ∑ i ∈ s1, w1 i = 1
hw2 : ∑ i ∈ s2, w2 i = 1
heq : (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2
i : ι
hi : i ∉ ↑s1 ∪ ↑s2
⊢ i ∈ s1 → w1 i = 0

Proof state:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
⊢ w i0 = 0

Tactic:
have hw1s : s.affineCombination k p w1 = p i0 :=
  s.affineCombination_of_eq_one_of_eq_zero w1 p hi0 (Function.update_self ..)
    fun _ _ hne => Function.update_of_ne hne ..

Result:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
hw1s : (affineCombination k s p) w1 = p i0
⊢ w i0 = 0

Proof state:
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha : AffineIndependent k p
s1 s2 : Finset ι
w1 w2 : ι → k
hw1 : ∑ i ∈ s1, w1 i = 1
hw2 : ∑ i ∈ s2, w2 i = 1
heq : (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2
i : ι
hi : i ∉ ↑s1 ∪ ↑s2
h : i ∈ s1
x✝ : ¬w1 i = 0
⊢ False

Tactic:
exact (mt (@Set.mem_union_left _ i ↑s1 ↑s2) hi) h

Result:
no goals

Proof state:
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
hw1s : (affineCombination k s p) w1 = p i0
w2 : ι → k := w + w1
⊢ ∑ i ∈ s, w2 i = 1

Tactic:
simp_all only [w2, Pi.add_apply, Finset.sum_add_distrib, zero_add]

Result:
no goals

Proof state:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
⊢ w i0 = 0

Tactic:
have hw1 : ∑ i ∈ s, w1 i = 1 := by
  rw [Finset.sum_update_of_mem hi0]
  simp only [Finset.sum_const_zero, add_zero, const_apply]

Result:
case mpr
k : Type u_1
V : Type u_2
P : Type u_3
inst✝³ : Ring k
inst✝² : AddCommGroup V
inst✝¹ : Module k V
inst✝ : AffineSpace V P
ι : Type u_4
p : ι → P
ha :
  ∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
    ∑ i ∈ s1, w1 i = 1 →
      ∑ i ∈ s2, w2 i = 1 →
        (affineCombination k s1 p) w1 = (affineCombination k s2 p) w2 → (↑s1).indicator w1 = (↑s2).indicator w2
s : Finset ι
w : ι → k
hw : ∑ i ∈ s, w i = 0
hs : (s.weightedVSub p) w = 0
i0 : ι
hi0 : i0 ∈ s
w1 : ι → k := update (const ι 0) i0 1
hw1 : ∑ i ∈ s, w1 i = 1
⊢ w i0 = 0