l3lab/ntp-mathlib huggingface dataset:
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      

Proof state:
case right
a b : Cardinal.{u_1}
h : a * b = a
ha : ℵ₀ ≤ a
this : a ≠ 0
⊢ b ≤ a ∧ b ≠ 0

Next tactic:
constructor
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · 

Proof state:
case right.left
a b : Cardinal.{u_1}
h : a * b = a
ha : ℵ₀ ≤ a
this : a ≠ 0
⊢ b ≤ a

Next tactic:
rw [← not_lt]
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        

Proof state:
case right.left
a b : Cardinal.{u_1}
h : a * b = a
ha : ℵ₀ ≤ a
this : a ≠ 0
⊢ ¬a < b

Next tactic:
exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · 

Proof state:
case right.right
a b : Cardinal.{u_1}
h : a * b = a
ha : ℵ₀ ≤ a
this : a ≠ 0
⊢ b ≠ 0

Next tactic:
rintro rfl
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        

Proof state:
case right.right
a : Cardinal.{u_1}
ha : ℵ₀ ≤ a
this : a ≠ 0
h : a * 0 = a
⊢ False

Next tactic:
apply this
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        

Proof state:
case right.right
a : Cardinal.{u_1}
ha : ℵ₀ ≤ a
this : a ≠ 0
h : a * 0 = a
⊢ a = 0

Next tactic:
rw [mul_zero] at h
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        

Proof state:
case right.right
a : Cardinal.{u_1}
ha : ℵ₀ ≤ a
this : a ≠ 0
h : 0 = a
⊢ a = 0

Next tactic:
exact h.symm
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    

Proof state:
case refine'_1.inr
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
⊢ (ℵ₀ ≤ a ∧ b ≤ a) ∧ b ≠ 0 ∨ b = 1 ∨ a = 0

Next tactic:
right
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    

Proof state:
case refine'_1.inr.h
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
⊢ b = 1 ∨ a = 0

Next tactic:
by_cases h2a : a = 0
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · 

Proof state:
case pos
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
h2a : a = 0
⊢ b = 1 ∨ a = 0

Next tactic:
exact Or.inr h2a
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    

Proof state:
case neg
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
h2a : ¬a = 0
⊢ b = 1 ∨ a = 0

Next tactic:
have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      

Proof state:
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
h2a : ¬a = 0
⊢ b ≠ 0

Next tactic:
rintro rfl
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      

Proof state:
a : Cardinal.{u_1}
ha : a < ℵ₀
h2a : ¬a = 0
h : a * 0 = a
⊢ False

Next tactic:
apply h2a
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      

Proof state:
a : Cardinal.{u_1}
ha : a < ℵ₀
h2a : ¬a = 0
h : a * 0 = a
⊢ a = 0

Next tactic:
rw [mul_zero] at h
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      

Proof state:
a : Cardinal.{u_1}
ha : a < ℵ₀
h2a : ¬a = 0
h : 0 = a
⊢ a = 0

Next tactic:
exact h.symm
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    

Proof state:
case neg
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
h2a : ¬a = 0
hb : b ≠ 0
⊢ b = 1 ∨ a = 0

Next tactic:
left
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    

Proof state:
case neg.h
a b : Cardinal.{u_1}
h : a * b = a
ha : a < ℵ₀
h2a : ¬a = 0
hb : b ≠ 0
⊢ b = 1

Next tactic:
rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    

Proof state:
case neg.h
a b : Cardinal.{u_1}
h : a * b = a
ha : a = 0 ∨ b = 0 ∨ (∃ n, a = ↑n) ∧ ∃ n, b = ↑n
h2a : ¬a = 0
hb : b ≠ 0
⊢ b = 1

Next tactic:
rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    

Proof state:
case neg.h.inl
b : Cardinal.{u_1}
hb : b ≠ 0
h : 0 * b = 0
h2a : ¬0 = 0
⊢ b = 1
case neg.h.inr.inl
a : Cardinal.{u_1}
h2a : ¬a = 0
h : a * 0 = a
hb : 0 ≠ 0
⊢ 0 = 1
case neg.h.inr.inr.intro.intro.intro n : ℕ h2a : ¬↑n = 0 m : ℕ hb : ↑m ≠ 0 h : ↑n * ↑m = ↑n ⊢ ↑m = 1

Next tactic:
contradiction
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    

Proof state:
case neg.h.inr.inl
a : Cardinal.{u_1}
h2a : ¬a = 0
h : a * 0 = a
hb : 0 ≠ 0
⊢ 0 = 1
case neg.h.inr.inr.intro.intro.intro n : ℕ h2a : ¬↑n = 0 m : ℕ hb : ↑m ≠ 0 h : ↑n * ↑m = ↑n ⊢ ↑m = 1

Next tactic:
contradiction
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    

Proof state:
case neg.h.inr.inr.intro.intro.intro
n : ℕ
h2a : ¬↑n = 0
m : ℕ
hb : ↑m ≠ 0
h : ↑n * ↑m = ↑n
⊢ ↑m = 1

Next tactic:
rw [← Ne] at h2a
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    

Proof state:
case neg.h.inr.inr.intro.intro.intro
n : ℕ
h2a : ↑n ≠ 0
m : ℕ
hb : ↑m ≠ 0
h : ↑n * ↑m = ↑n
⊢ ↑m = 1

Next tactic:
rw [← one_le_iff_ne_zero] at h2a hb
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    

Proof state:
case neg.h.inr.inr.intro.intro.intro
n : ℕ
h2a : 1 ≤ ↑n
m : ℕ
hb : 1 ≤ ↑m
h : ↑n * ↑m = ↑n
⊢ ↑m = 1

Next tactic:
norm_cast at h2a hb h ⊢
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    norm_cast at h2a hb h ⊢
    

Proof state:
case neg.h.inr.inr.intro.intro.intro
n m : ℕ
h2a : 1 ≤ n
hb : 1 ≤ m
h : n * m = n
⊢ m = 1

Next tactic:
apply le_antisymm _ hb
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    norm_cast at h2a hb h ⊢
    apply le_antisymm _ hb
    

Proof state:
n m : ℕ
h2a : 1 ≤ n
hb : 1 ≤ m
h : n * m = n
⊢ m ≤ 1

Next tactic:
rw [← not_lt]
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    norm_cast at h2a hb h ⊢
    apply le_antisymm _ hb
    rw [← not_lt]
    

Proof state:
n m : ℕ
h2a : 1 ≤ n
hb : 1 ≤ m
h : n * m = n
⊢ ¬1 < m

Next tactic:
apply fun h2b => ne_of_gt _ h
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    norm_cast at h2a hb h ⊢
    apply le_antisymm _ hb
    rw [← not_lt]
    apply fun h2b => ne_of_gt _ h
    

Proof state:
n m : ℕ
h2a : 1 ≤ n
hb : 1 ≤ m
h : n * m = n
⊢ 1 < m → n < n * m

Next tactic:
conv_rhs => left; rw [← mul_one n]
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    norm_cast at h2a hb h ⊢
    apply le_antisymm _ hb
    rw [← not_lt]
    apply fun h2b => ne_of_gt _ h
    conv_rhs => 

Proof state:
case h₂
n m : ℕ
h2a : 1 ≤ n
hb : 1 ≤ m
h : n * m = n
| n < n * m

Next tactic:
left; rw [← mul_one n]
theorem mul_eq_left_iff {a b : Cardinal} : a * b = a ↔ max ℵ₀ b ≤ a ∧ b ≠ 0 ∨ b = 1 ∨ a = 0 := by
  rw [max_le_iff]
  refine' ⟨fun h => _, _⟩
  · rcases le_or_lt ℵ₀ a with ha | ha
    · have : a ≠ 0 := by
        rintro rfl
        exact ha.not_lt aleph0_pos
      left
      rw [and_assoc]
      use ha
      constructor
      · rw [← not_lt]
        exact fun hb => ne_of_gt (hb.trans_le (le_mul_left this)) h
      · rintro rfl
        apply this
        rw [mul_zero] at h
        exact h.symm
    right
    by_cases h2a : a = 0
    · exact Or.inr h2a
    have hb : b ≠ 0 := by
      rintro rfl
      apply h2a
      rw [mul_zero] at h
      exact h.symm
    left
    rw [← h, mul_lt_aleph0_iff, lt_aleph0, lt_aleph0] at ha
    rcases ha with (rfl | rfl | ⟨⟨n, rfl⟩, ⟨m, rfl⟩⟩)
    contradiction
    contradiction
    rw [← Ne] at h2a
    rw [← one_le_iff_ne_zero] at h2a hb
    norm_cast at h2a hb h ⊢
    apply le_antisymm _ hb
    rw [← not_lt]
    apply fun h2b => ne_of_gt _ h
    conv_rhs => 

Proof state:
case h₂
n m : ℕ
h2a : 1 ≤ n
hb : 1 ≤ m
h : n * m = n
| n < n * m

Next tactic:
left