-- Mathlib/GroupTheory/Coxeter/Basic.lean
theorem simple_induction_right {p : W → Prop} (w : W) (one : p 1)
    (mul_simple_right : ∀ (w : W) (i : B), p w → p (w * s i)) : p w

Proof state:
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
⊢ p w

Tactic:
let p' : ((w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop) :=
  fun w _ ↦ p w

Result:
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
⊢ p w

Proof state:
case h
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ w ∈ Submonoid.closure (Set.range cs.simple)

Tactic:
exact this

Result:
no goals

Proof state:
case mul_right.intro
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
x : W
hx✝ : x ∈ Submonoid.closure (Set.range cs.simple)
i : B
⊢ p' x hx✝ → p' (x * cs.simple i) ⋯

Tactic:
exact mul_simple_right x i

Result:
no goals

Proof state:
case one
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ p' 1 ⋯

Tactic:
exact one

Result:
no goals

Proof state:
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
⊢ p w

Tactic:
have := cs.submonoid_closure_range_simple.symm ▸ Submonoid.mem_top w

Result:
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ p w

Proof state:
case mul_right
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ ∀ (x : W) (hx : x ∈ Submonoid.closure (Set.range cs.simple)) (y : W) (hy : y ∈ Set.range cs.simple),
    p' x hx → p' (x * y) ⋯

Tactic:
rintro x _ _ ⟨i, rfl⟩

Result:
case mul_right.intro
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
x : W
hx✝ : x ∈ Submonoid.closure (Set.range cs.simple)
i : B
⊢ p' x hx✝ → p' (x * cs.simple i) ⋯

Proof state:
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ p w

Tactic:
apply Submonoid.closure_induction_right (p := p')

Result:
case one
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ p' 1 ⋯

case mul_right
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ ∀ (x : W) (hx : x ∈ Submonoid.closure (Set.range cs.simple)) (y : W) (hy : y ∈ Set.range cs.simple),
    p' x hx → p' (x * y) ⋯

case h
B : Type u_1
W : Type u_3
inst✝ : Group W
M : CoxeterMatrix B
cs : CoxeterSystem M W
p : W → Prop
w : W
one : p 1
mul_simple_right : ∀ (w : W) (i : B), p w → p (w * cs.simple i)
p' : (w : W) → w ∈ Submonoid.closure (Set.range cs.simple) → Prop := fun w x => p w
this : w ∈ Submonoid.closure (Set.range cs.simple)
⊢ w ∈ Submonoid.closure (Set.range cs.simple)