Theorem: Monoid.CoprodI.Word.mem_smul_iff
File: Mathlib/GroupTheory/CoprodI.lean

Proof steps:
state_before: ι : Type u_1
M : ι → Type u_2
inst✝³ : (i : ι) → Monoid (M i)
N : Type u_3
inst✝² : Monoid N
inst✝¹ : (i : ι) → DecidableEq (M i)
inst✝ : DecidableEq ι
i j : ι
m₁ : M i
m₂ : M j
w : Word M
⊢ ⟨i, m₁⟩ ∈ (of m₂ • w).toList ↔
    ¬i = j ∧ ⟨i, m₁⟩ ∈ w.toList ∨
      m₁ ≠ 1 ∧
        ∃ (hij : i = j),
          ⟨i, m₁⟩ ∈ w.toList.tail ∨
            (∃ m', ⟨j, m'⟩ ∈ w.toList.head? ∧ m₁ = ⋯ ▸ (m₂ * m')) ∨ w.fstIdx ≠ some j ∧ m₁ = ⋯ ▸ m₂
state_after: ι : Type u_1
M : ι → Type u_2
inst✝³ : (i : ι) → Monoid (M i)
N : Type u_3
inst✝² : Monoid N
inst✝¹ : (i : ι) → DecidableEq (M i)
inst✝ : DecidableEq ι
i j : ι
m₁ : M i
m₂ : M j
w : Word M
⊢ (⟨i, m₁⟩ ∈ w.toList.tail ∨
      (i ≠ j ∧ ∃ (h : w.toList ≠ []), w.toList.head h = ⟨i, m₁⟩) ∨
        m₁ ≠ 1 ∧
          ∃ (h : j = i),
            m₁ =
              h ▸
                (let __src := (equivPair j) w;
                  {
                    head :=
                      m₂ *
                        if h : ∃ (h : w.toList ≠ []), (w.toList.head h).fst = j then ⋯ ▸ (w.toList.head ⋯).snd else 1,
                    tail := __src.tail, fstIdx_ne := ⋯ }).head) ↔
    ¬i = j ∧ ⟨i, m₁⟩ ∈ w.toList ∨
      m₁ ≠ 1 ∧
        ∃ (hij : i = j),
          ⟨i, m₁⟩ ∈ w.toList.tail ∨
            (∃ m', ⟨j, m'⟩ ∈ w.toList.head? ∧ m₁ = ⋯ ▸ (m₂ * m')) ∨ w.fstIdx ≠ some j ∧ m₁ = ⋯ ▸ m₂
tactic: rw [of_smul_def, mem_rcons_iff, mem_equivPair_tail_iff, equivPair_head, or_assoc]
state_before: ι : Type u_1
M : ι → Type u_2
inst✝³ : (i : ι) → Monoid (M i)
N : Type u_3
inst✝² : Monoid N
inst✝¹ : (i : ι) → DecidableEq (M i)
inst✝ : DecidableEq ι
i j : ι
m₁ : M i
m₂ : M j
w : Word M
⊢ (⟨i, m₁⟩ ∈ w.toList.tail ∨
      (i ≠ j ∧ ∃ (h : w.toList ≠ []), w.toList.head h = ⟨i, m₁⟩) ∨
        m₁ ≠ 1 ∧
          ∃ (h : j = i),
            m₁ =
              h ▸
                (let __src := (equivPair j) w;
                  {
                    head :=
                      m₂ *
                        if h : ∃ (h : w.toList ≠ []), (w.toList.head h).fst = j then ⋯ ▸ (w.toList.head ⋯).snd else 1,
                    tail := __src.tail, fstIdx_ne := ⋯ }).head) ↔
    ¬i = j ∧ ⟨i, m₁⟩ ∈ w.toList ∨
      m₁ ≠ 1 ∧
        ∃ (hij : i = j),
          ⟨i, m₁⟩ ∈ w.toList.tail ∨
            (∃ m', ⟨j, m'⟩ ∈ w.toList.head? ∧ m₁ = ⋯ ▸ (m₂ * m')) ∨ w.fstIdx ≠ some j ∧ m₁ = ⋯ ▸ m₂
state_after: case pos
ι : Type u_1
M : ι → Type u_2
inst✝³ : (i : ι) → Monoid (M i)
N : Type u_3
inst✝² : Monoid N
inst✝¹ : (i : ι) → DecidableEq (M i)
inst✝ : DecidableEq ι
i j : ι
m₁ : M i
m₂ : M j
w : Word M
hij : i = j
⊢ (⟨i, m₁⟩ ∈ w.toList.tail ∨
      (i ≠ j ∧ ∃ (h : w.toList ≠ []), w.toList.head h = ⟨i, m₁⟩) ∨
        m₁ ≠ 1 ∧
          ∃ (h : j = i),
            m₁ =
              h ▸
                (let __src := (equivPair j) w;
                  {
                    head :=
                      m₂ *
                        if h : ∃ (h : w.toList ≠ []), (w.toList.head h).fst = j then ⋯ ▸ (w.toList.head ⋯).snd else 1,
                    tail := __src.tail, fstIdx_ne := ⋯ }).head) ↔
    ¬i = j ∧ ⟨i, m₁⟩ ∈ w.toList ∨
      m₁ ≠ 1 ∧
        ∃ (hij : i = j),
          ⟨i, m₁⟩ ∈ w.toList.tail ∨
            (∃ m', ⟨j, m'⟩ ∈ w.toList.head? ∧ m₁ = ⋯ ▸ (m₂ * m')) ∨ w.fstIdx ≠ some j ∧ m₁ = ⋯ ▸ m₂

case neg
ι : Type u_1
M : ι → Type u_2
inst✝³ : (i : ι) → Monoid (M i)
N : Type u_3
inst✝² : Monoid N
inst✝¹ : (i : ι) → DecidableEq (M i)
inst✝ : DecidableEq ι
i j : ι
m₁ : M i
m₂ : M j
w : Word M
hij : ¬i = j
⊢ (⟨i, m₁⟩ ∈ w.toList.tail ∨
      (i ≠ j ∧ ∃ (h : w.toList ≠ []), w.toList.head h = ⟨i, m₁⟩) ∨
        m₁ ≠ 1 ∧
          ∃ (h : j = i),
            m₁ =
              h ▸
                (let __src := (equivPair j) w;
                  {
                    head :=
                      m₂ *
                        if h : ∃ (h : w.toList ≠ []), (w.toList.head h).fst = j then ⋯ ▸ (w.toList.head ⋯).snd else 1,
                    tail := __src.tail, fstIdx_ne := ⋯ }).head) ↔
    ¬i = j ∧ ⟨i, m₁⟩ ∈ w.toList ∨
      m₁ ≠ 1 ∧
        ∃ (hij : i = j),
          ⟨i, m₁⟩ ∈ w.toList.tail ∨
            (∃ m', ⟨j, m'⟩ ∈ w.toList.head? ∧ m₁ = ⋯ ▸ (m₂ * m')) ∨ w.fstIdx ≠ some j ∧ m₁ = ⋯ ▸ m₂
tactic: by_cases hij : i = j