-- Mathlib/Analysis/Convex/Combination.lean
theorem Convex.centerMass_mem (hs : Convex R s) :
    (∀ i ∈ t, 0 ≤ w i) → (0 < ∑ i ∈ t, w i) → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s

Proof state:
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
⊢ (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s

Tactic:
induction' t using Finset.induction with i t hi ht

Result:
case empty
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
⊢ (∀ i ∈ ∅, 0 ≤ w i) → 0 < ∑ i ∈ ∅, w i → (∀ i ∈ ∅, z i ∈ s) → ∅.centerMass w z ∈ s

case insert
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
⊢ (∀ i_1 ∈ insert i t, 0 ≤ w i_1) →
    0 < ∑ i ∈ insert i t, w i → (∀ i_1 ∈ insert i t, z i_1 ∈ s) → (insert i t).centerMass w z ∈ s

Proof state:
case neg.refine_1
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ¬∑ j ∈ t, w j = 0
⊢ 0 < ∑ i ∈ t, w i

Tactic:
exact lt_of_le_of_ne (sum_nonneg hs₀) (Ne.symm hsum_t)

Result:
no goals

Proof state:
case neg
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ¬∑ j ∈ t, w j = 0
⊢ (insert i t).centerMass w z ∈ s

Tactic:
rw [Finset.centerMass_insert _ _ _ hi hsum_t]

Result:
case neg
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ¬∑ j ∈ t, w j = 0
⊢ (w i / (w i + ∑ j ∈ t, w j)) • z i + ((∑ j ∈ t, w j) / (w i + ∑ j ∈ t, w j)) • t.centerMass w z ∈ s

Proof state:
case pos
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ∑ j ∈ t, w j = 0
ws : ∀ j ∈ t, w j = 0
⊢ (insert i t).centerMass w z ∈ s

Tactic:
have wz : ∑ j ∈ t, w j • z j = 0 := sum_eq_zero fun i hi => by simp [ws i hi]

Result:
case pos
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ∑ j ∈ t, w j = 0
ws : ∀ j ∈ t, w j = 0
wz : ∑ j ∈ t, w j • z j = 0
⊢ (insert i t).centerMass w z ∈ s

Proof state:
case insert
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < ∑ i ∈ insert i t, w i
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
⊢ (insert i t).centerMass w z ∈ s

Tactic:
have hs₀ : ∀ j ∈ t, 0 ≤ w j := fun j hj => h₀ j <| mem_insert_of_mem hj

Result:
case insert
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < ∑ i ∈ insert i t, w i
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
⊢ (insert i t).centerMass w z ∈ s

Proof state:
case pos
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ∑ j ∈ t, w j = 0
⊢ (insert i t).centerMass w z ∈ s

Tactic:
have ws : ∀ j ∈ t, w j = 0 := (sum_eq_zero_iff_of_nonneg hs₀).1 hsum_t

Result:
case pos
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i : ι
t : Finset ι
hi : i ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i_1 ∈ insert i t, 0 ≤ w i_1
hpos : 0 < w i + ∑ x ∈ t, w x
hmem : ∀ i_1 ∈ insert i t, z i_1 ∈ s
zi : z i ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ∑ j ∈ t, w j = 0
ws : ∀ j ∈ t, w j = 0
⊢ (insert i t).centerMass w z ∈ s

Proof state:
R : Type u_1
E : Type u_3
ι : Type u_5
inst✝² : LinearOrderedField R
inst✝¹ : AddCommGroup E
inst✝ : Module R E
s : Set E
t✝ : Finset ι
w : ι → R
z : ι → E
hs : Convex R s
i✝ : ι
t : Finset ι
hi✝ : i✝ ∉ t
ht : (∀ i ∈ t, 0 ≤ w i) → 0 < ∑ i ∈ t, w i → (∀ i ∈ t, z i ∈ s) → t.centerMass w z ∈ s
h₀ : ∀ i ∈ insert i✝ t, 0 ≤ w i
hpos : 0 < w i✝ + ∑ x ∈ t, w x
hmem : ∀ i ∈ insert i✝ t, z i ∈ s
zi : z i✝ ∈ s
hs₀ : ∀ j ∈ t, 0 ≤ w j
hsum_t : ∑ j ∈ t, w j = 0
ws : ∀ j ∈ t, w j = 0
i : ι
hi : i ∈ t
⊢ w i • z i = 0

Tactic:
simp [ws i hi]

Result:
no goals