l3lab/ntp-mathlib huggingface dataset:
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative on all products of primes. -/
-- @[elab_as_elim] Porting note: commented out
theorem multiplicative_prime_power {f : α → β} (s : Finset α) (i j : α → ℕ)
    (is_prime : ∀ p ∈ s, Prime p) (is_coprime : ∀ᵉ (p ∈ s) (q ∈ s), p ∣ q → p = q)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p) := by
  letI := Classical.decEq α
  induction' s using Finset.induction_on with p s hps ih
  · simpa using h1 isUnit_one
  have hpr_p := is_prime _ (Finset.mem_insert_self _ _)
  

Proof state:
case insert
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
i j : α → ℕ
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
p : α
s : Finset α
hps : p ∉ s
ih :
  (∀ p ∈ s, Prime p) →
    (∀ p ∈ s, ∀ q ∈ s, p ∣ q → p = q) → f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p)
is_prime : ∀ p_1 ∈ insert p s, Prime p_1
is_coprime : ∀ p_1 ∈ insert p s, ∀ q ∈ insert p s, p_1 ∣ q → p_1 = q
hpr_p : Prime p
⊢ f (∏ p in insert p s, p ^ (i p + j p)) = f (∏ p in insert p s, p ^ i p) * f (∏ p in insert p s, p ^ j p)

Next tactic:
have hpr_s : ∀ p ∈ s, Prime p := fun p hp => is_prime _ (Finset.mem_insert_of_mem hp)
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative on all products of primes. -/
-- @[elab_as_elim] Porting note: commented out
theorem multiplicative_prime_power {f : α → β} (s : Finset α) (i j : α → ℕ)
    (is_prime : ∀ p ∈ s, Prime p) (is_coprime : ∀ᵉ (p ∈ s) (q ∈ s), p ∣ q → p = q)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p) := by
  letI := Classical.decEq α
  induction' s using Finset.induction_on with p s hps ih
  · simpa using h1 isUnit_one
  have hpr_p := is_prime _ (Finset.mem_insert_self _ _)
  have hpr_s : ∀ p ∈ s, Prime p := fun p hp => is_prime _ (Finset.mem_insert_of_mem hp)
  

Proof state:
case insert
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
i j : α → ℕ
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
p : α
s : Finset α
hps : p ∉ s
ih :
  (∀ p ∈ s, Prime p) →
    (∀ p ∈ s, ∀ q ∈ s, p ∣ q → p = q) → f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p)
is_prime : ∀ p_1 ∈ insert p s, Prime p_1
is_coprime : ∀ p_1 ∈ insert p s, ∀ q ∈ insert p s, p_1 ∣ q → p_1 = q
hpr_p : Prime p
hpr_s : ∀ p ∈ s, Prime p
⊢ f (∏ p in insert p s, p ^ (i p + j p)) = f (∏ p in insert p s, p ^ i p) * f (∏ p in insert p s, p ^ j p)

Next tactic:
have hcp_p := fun i => prime_pow_coprime_prod_of_coprime_insert i p hps is_prime is_coprime
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative on all products of primes. -/
-- @[elab_as_elim] Porting note: commented out
theorem multiplicative_prime_power {f : α → β} (s : Finset α) (i j : α → ℕ)
    (is_prime : ∀ p ∈ s, Prime p) (is_coprime : ∀ᵉ (p ∈ s) (q ∈ s), p ∣ q → p = q)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p) := by
  letI := Classical.decEq α
  induction' s using Finset.induction_on with p s hps ih
  · simpa using h1 isUnit_one
  have hpr_p := is_prime _ (Finset.mem_insert_self _ _)
  have hpr_s : ∀ p ∈ s, Prime p := fun p hp => is_prime _ (Finset.mem_insert_of_mem hp)
  have hcp_p := fun i => prime_pow_coprime_prod_of_coprime_insert i p hps is_prime is_coprime
  

Proof state:
case insert
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
i j : α → ℕ
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
p : α
s : Finset α
hps : p ∉ s
ih :
  (∀ p ∈ s, Prime p) →
    (∀ p ∈ s, ∀ q ∈ s, p ∣ q → p = q) → f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p)
is_prime : ∀ p_1 ∈ insert p s, Prime p_1
is_coprime : ∀ p_1 ∈ insert p s, ∀ q ∈ insert p s, p_1 ∣ q → p_1 = q
hpr_p : Prime p
hpr_s : ∀ p ∈ s, Prime p
hcp_p : ∀ (i : α → ℕ) (q : α), q ∣ p ^ i p → q ∣ ∏ p' in s, p' ^ i p' → IsUnit q
⊢ f (∏ p in insert p s, p ^ (i p + j p)) = f (∏ p in insert p s, p ^ i p) * f (∏ p in insert p s, p ^ j p)

Next tactic:
have hcp_s : ∀ᵉ (p ∈ s) (q ∈ s), p ∣ q → p = q := fun p hp q hq =>
    is_coprime p (Finset.mem_insert_of_mem hp) q (Finset.mem_insert_of_mem hq)
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative on all products of primes. -/
-- @[elab_as_elim] Porting note: commented out
theorem multiplicative_prime_power {f : α → β} (s : Finset α) (i j : α → ℕ)
    (is_prime : ∀ p ∈ s, Prime p) (is_coprime : ∀ᵉ (p ∈ s) (q ∈ s), p ∣ q → p = q)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p) := by
  letI := Classical.decEq α
  induction' s using Finset.induction_on with p s hps ih
  · simpa using h1 isUnit_one
  have hpr_p := is_prime _ (Finset.mem_insert_self _ _)
  have hpr_s : ∀ p ∈ s, Prime p := fun p hp => is_prime _ (Finset.mem_insert_of_mem hp)
  have hcp_p := fun i => prime_pow_coprime_prod_of_coprime_insert i p hps is_prime is_coprime
  have hcp_s : ∀ᵉ (p ∈ s) (q ∈ s), p ∣ q → p = q := fun p hp q hq =>
    is_coprime p (Finset.mem_insert_of_mem hp) q (Finset.mem_insert_of_mem hq)
  

Proof state:
case insert
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
i j : α → ℕ
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
p : α
s : Finset α
hps : p ∉ s
ih :
  (∀ p ∈ s, Prime p) →
    (∀ p ∈ s, ∀ q ∈ s, p ∣ q → p = q) → f (∏ p in s, p ^ (i p + j p)) = f (∏ p in s, p ^ i p) * f (∏ p in s, p ^ j p)
is_prime : ∀ p_1 ∈ insert p s, Prime p_1
is_coprime : ∀ p_1 ∈ insert p s, ∀ q ∈ insert p s, p_1 ∣ q → p_1 = q
hpr_p : Prime p
hpr_s : ∀ p ∈ s, Prime p
hcp_p : ∀ (i : α → ℕ) (q : α), q ∣ p ^ i p → q ∣ ∏ p' in s, p' ^ i p' → IsUnit q
hcp_s : ∀ p ∈ s, ∀ q ∈ s, p ∣ q → p = q
⊢ f (∏ p in insert p s, p ^ (i p + j p)) = f (∏ p in insert p s, p ^ i p) * f (∏ p in insert p s, p ^ j p)

Next tactic:
rw [Finset.prod_insert hps, Finset.prod_insert hps, Finset.prod_insert hps, hcp (hcp_p _),
    hpr _ hpr_p, hcp (hcp_p _), hpr _ hpr_p, hcp (hcp_p (fun p => i p + j p)), hpr _ hpr_p,
    ih hpr_s hcp_s, pow_add, mul_assoc, mul_left_comm (f p ^ j p), mul_assoc]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  

Proof state:
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
⊢ f (a * b) = f a * f b

Next tactic:
letI := Classical.decEq α
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  

Proof state:
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
⊢ f (a * b) = f a * f b

Next tactic:
by_cases ha0 : a = 0
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · 

Proof state:
case pos
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : a = 0
⊢ f (a * b) = f a * f b

Next tactic:
rw [ha0, zero_mul, h0, zero_mul]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  

Proof state:
case neg
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
⊢ f (a * b) = f a * f b

Next tactic:
by_cases hb0 : b = 0
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · 

Proof state:
case pos
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : b = 0
⊢ f (a * b) = f a * f b

Next tactic:
rw [hb0, mul_zero, h0, mul_zero]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  

Proof state:
case neg
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
⊢ f (a * b) = f a * f b

Next tactic:
by_cases hf1 : f 1 = 0
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  by_cases hf1 : f 1 = 0
  · 

Proof state:
case pos
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
hf1 : f 1 = 0
⊢ f (a * b) = f a * f b

Next tactic:
calc
      f (a * b) = f (a * b * 1) := by rw [mul_one]
      _ = 0 := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f (b * 1) := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f b := by rw [mul_one]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  by_cases hf1 : f 1 = 0
  · calc
      f (a * b) = f (a * b * 1) := by 

Proof state:
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
hf1 : f 1 = 0
⊢ f (a * b) = f (a * b * 1)

Next tactic:
rw [mul_one]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  by_cases hf1 : f 1 = 0
  · calc
      f (a * b) = f (a * b * 1) := by rw [mul_one]
      _ = 0 := by 

Proof state:
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
hf1 : f 1 = 0
⊢ f (a * b * 1) = 0

Next tactic:
simp only [h1 isUnit_one, hf1, mul_zero]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  by_cases hf1 : f 1 = 0
  · calc
      f (a * b) = f (a * b * 1) := by rw [mul_one]
      _ = 0 := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f (b * 1) := by 

Proof state:
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
hf1 : f 1 = 0
⊢ 0 = f a * f (b * 1)

Next tactic:
simp only [h1 isUnit_one, hf1, mul_zero]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  by_cases hf1 : f 1 = 0
  · calc
      f (a * b) = f (a * b * 1) := by rw [mul_one]
      _ = 0 := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f (b * 1) := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f b := by 

Proof state:
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
hf1 : f 1 = 0
⊢ f a * f (b * 1) = f a * f b

Next tactic:
rw [mul_one]
/-- If `f` maps `p ^ i` to `(f p) ^ i` for primes `p`, and `f`
is multiplicative on coprime elements, then `f` is multiplicative everywhere. -/
theorem multiplicative_of_coprime (f : α → β) (a b : α) (h0 : f 0 = 0)
    (h1 : ∀ {x y}, IsUnit y → f (x * y) = f x * f y)
    (hpr : ∀ {p} (i : ℕ), Prime p → f (p ^ i) = f p ^ i)
    (hcp : ∀ {x y}, (∀ p, p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y) :
    f (a * b) = f a * f b := by
  letI := Classical.decEq α
  by_cases ha0 : a = 0
  · rw [ha0, zero_mul, h0, zero_mul]
  by_cases hb0 : b = 0
  · rw [hb0, mul_zero, h0, mul_zero]
  by_cases hf1 : f 1 = 0
  · calc
      f (a * b) = f (a * b * 1) := by rw [mul_one]
      _ = 0 := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f (b * 1) := by simp only [h1 isUnit_one, hf1, mul_zero]
      _ = f a * f b := by rw [mul_one]
  

Proof state:
case neg
α : Type u_1
R : Type u_2
inst✝⁴ : CancelCommMonoidWithZero R
inst✝³ : UniqueFactorizationMonoid R
inst✝² : CancelCommMonoidWithZero α
inst✝¹ : UniqueFactorizationMonoid α
β : Type u_3
inst✝ : CancelCommMonoidWithZero β
f : α → β
a b : α
h0 : f 0 = 0
h1 : ∀ {x y : α}, IsUnit y → f (x * y) = f x * f y
hpr : ∀ {p : α} (i : ℕ), Prime p → f (p ^ i) = f p ^ i
hcp : ∀ {x y : α}, (∀ (p : α), p ∣ x → p ∣ y → IsUnit p) → f (x * y) = f x * f y
this : DecidableEq α := Classical.decEq α
ha0 : ¬a = 0
hb0 : ¬b = 0
hf1 : ¬f 1 = 0
⊢ f (a * b) = f a * f b

Next tactic:
haveI : Nontrivial α := ⟨⟨_, _, ha0⟩⟩