-- Mathlib/RingTheory/ChainOfDivisors.lean
theorem pow_image_of_prime_by_factor_orderIso_dvd
    {m p : Associates M} {n : Associates N} (hn : n ≠ 0) (hp : p ∈ normalizedFactors m)
    (d : Set.Iic m ≃o Set.Iic n) {s : ℕ} (hs' : p ^ s ≤ m) :
    (d ⟨p, dvd_of_mem_normalizedFactors hp⟩ : Associates N) ^ s ≤ n

Proof state:
case neg.intro.intro.intro.refine_3
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
c₂ : Fin (s + 1) → Associates N := fun t => ↑(d ⟨c₁ t, ⋯⟩)
c₂_def : ∀ (t : Fin (s + 1)), c₂ t = ↑(d ⟨c₁ t, ⋯⟩)
r : Associates N
⊢ (∃ i, r = c₂ i) → r ≤ ↑(d ⟨c₁ 1 ^ s, hs'⟩)

Tactic:
rintro ⟨i, hr⟩

Result:
case neg.intro.intro.intro.refine_3.intro
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
c₂ : Fin (s + 1) → Associates N := fun t => ↑(d ⟨c₁ t, ⋯⟩)
c₂_def : ∀ (t : Fin (s + 1)), c₂ t = ↑(d ⟨c₁ t, ⋯⟩)
r : Associates N
i : Fin (s + 1)
hr : r = c₂ i
⊢ r ≤ ↑(d ⟨c₁ 1 ^ s, hs'⟩)

Proof state:
case neg
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m p : Associates M
n : Associates N
hn : n ≠ 0
hp : p ∈ normalizedFactors m
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs' : p ^ s ≤ m
hs : ¬s = 0
⊢ ↑(d ⟨p, ⋯⟩) ^ s = ↑(d ⟨p ^ s, hs'⟩)

Tactic:
obtain ⟨c₁, rfl, hc₁', hc₁''⟩ := exists_chain_of_prime_pow hs (prime_of_normalized_factor p hp)

Result:
case neg.intro.intro.intro
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
⊢ ↑(d ⟨c₁ 1, ⋯⟩) ^ s = ↑(d ⟨c₁ 1 ^ s, hs'⟩)

Proof state:
case neg
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m p : Associates M
n : Associates N
hn : n ≠ 0
hp : p ∈ normalizedFactors m
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs' : p ^ s ≤ m
hs : ¬s = 0
⊢ ↑(d ⟨p, ⋯⟩) ^ s ≤ n

Tactic:
suffices (d ⟨p, dvd_of_mem_normalizedFactors hp⟩ : Associates N) ^ s =
    (d ⟨p ^ s, hs'⟩) by
  rw [this]
  apply Subtype.prop (d ⟨p ^ s, hs'⟩)

Result:
case neg
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m p : Associates M
n : Associates N
hn : n ≠ 0
hp : p ∈ normalizedFactors m
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs' : p ^ s ≤ m
hs : ¬s = 0
⊢ ↑(d ⟨p, ⋯⟩) ^ s = ↑(d ⟨p ^ s, hs'⟩)

Proof state:
case neg.intro.intro.intro.refine_1
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
c₂ : Fin (s + 1) → Associates N := fun t => ↑(d ⟨c₁ t, ⋯⟩)
c₂_def : ∀ (t : Fin (s + 1)), c₂ t = ↑(d ⟨c₁ t, ⋯⟩)
t u : Fin (s + 1)
h : t < u
⊢ c₂ t < c₂ u

Tactic:
rw [c₂_def, c₂_def, Subtype.coe_lt_coe, d.lt_iff_lt, Subtype.mk_lt_mk, hc₁'.lt_iff_lt]

Result:
case neg.intro.intro.intro.refine_1
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
c₂ : Fin (s + 1) → Associates N := fun t => ↑(d ⟨c₁ t, ⋯⟩)
c₂_def : ∀ (t : Fin (s + 1)), c₂ t = ↑(d ⟨c₁ t, ⋯⟩)
t u : Fin (s + 1)
h : t < u
⊢ t < u

Proof state:
case intro
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
c₂ : Fin (s + 1) → Associates N := fun t => ↑(d ⟨c₁ t, ⋯⟩)
c₂_def : ∀ (t : Fin (s + 1)), c₂ t = ↑(d ⟨c₁ t, ⋯⟩)
r : Associates N
hr : r ≤ ↑(d ⟨c₁ 1 ^ s, hs'⟩)
this✝ : r ≤ n
this : d.symm ⟨r, this✝⟩ ≤ ⟨c₁ 1 ^ s, hs'⟩
i : Fin (s + 1)
hi : ↑(d.symm ⟨r, this✝⟩) = c₁ i
⊢ ∃ i, r = c₂ i

Tactic:
use i

Result:
case h
M : Type u_1
inst✝³ : CancelCommMonoidWithZero M
N : Type u_2
inst✝² : CancelCommMonoidWithZero N
inst✝¹ : UniqueFactorizationMonoid N
inst✝ : UniqueFactorizationMonoid M
m : Associates M
n : Associates N
hn : n ≠ 0
d : ↑(Set.Iic m) ≃o ↑(Set.Iic n)
s : ℕ
hs : ¬s = 0
c₁ : Fin (s + 1) → Associates M
hp : c₁ 1 ∈ normalizedFactors m
hs' : c₁ 1 ^ s ≤ m
hc₁' : StrictMono c₁
hc₁'' : ∀ {r : Associates M}, r ≤ c₁ 1 ^ s ↔ ∃ i, r = c₁ i
c₂ : Fin (s + 1) → Associates N := fun t => ↑(d ⟨c₁ t, ⋯⟩)
c₂_def : ∀ (t : Fin (s + 1)), c₂ t = ↑(d ⟨c₁ t, ⋯⟩)
r : Associates N
hr : r ≤ ↑(d ⟨c₁ 1 ^ s, hs'⟩)
this✝ : r ≤ n
this : d.symm ⟨r, this✝⟩ ≤ ⟨c₁ 1 ^ s, hs'⟩
i : Fin (s + 1)
hi : ↑(d.symm ⟨r, this✝⟩) = c₁ i
⊢ r = c₂ i