Theorem: Regex.NFA.matches_of_path.alternate
Proof state before:
case intro.intro.intro.intro.intro.step
nfa : NFA
next : Fin nfa.nodes.size
r₁ r₂ : Expr
result : { nfa' // nfa.nodes.size < nfa'.nodes.size }
cs : List Char
eq : nfa.pushRegex next (r₁.alternate r₂) = result
ih₁ :
  ∀ {nfa : NFA} {next : Fin nfa.nodes.size} {result : { nfa' // nfa.nodes.size < nfa'.nodes.size }} {cs : List Char},
    nfa.pushRegex next r₁ = result →
      (↑result).pathToNext (↑next) nfa.nodes.size (↑(↑result).start) cs → Expr.matches cs r₁
ih₂ :
  ∀ {nfa : NFA} {next : Fin nfa.nodes.size} {result : { nfa' // nfa.nodes.size < nfa'.nodes.size }} {cs : List Char},
    nfa.pushRegex next r₂ = result →
      (↑result).pathToNext (↑next) nfa.nodes.size (↑(↑result).start) cs → Expr.matches cs r₂
nfa₁ : { nfa' // nfa.nodes.size < nfa'.nodes.size }
start₁ : Fin (↑nfa₁).nodes.size
nfa₂ : { nfa' // (↑nfa₁).nodes.size < nfa'.nodes.size }
start₂ : Fin (↑nfa₂).nodes.size
inBounds : (Node.split ↑start₁ ↑start₂).inBounds ((↑nfa₂).nodes.size + 1)
final : { nfa' // (↑nfa₂).nodes.size < nfa'.nodes.size }
property : nfa.nodes.size < (↑final).nodes.size
eq₁ : nfa₁ = nfa.pushRegex next r₁
eq₂ : start₁ = (↑nfa₁).start
eq₃ : nfa₂ = (↑nfa₁).pushRegex ⟨↑next, ⋯⟩ r₂
eq₄ : start₂ = (↑nfa₂).start
eq₅ : final = (↑nfa₂).pushNode (Node.split ↑start₁ ↑start₂) inBounds
eq' : result = ⟨↑final, property⟩
startNode : (↑final)[↑(↑final).start] = Node.split ↑start₁ ↑start₂
neStart₁ : ↑next ≠ ↑start₁
neStart₂ : ↑next ≠ ↑start₂
get₂ : ∀ (i : ℕ), nfa.nodes.size ≤ i → ∀ (h₂ : i < (↑nfa₂).nodes.size), (↑nfa₂)[i] = (↑final)[i]
get₁ : ∀ (i : ℕ), nfa.nodes.size ≤ i → ∀ (h₂ : i < (↑nfa₁).nodes.size), (↑nfa₁)[i] = (↑final)[i]
i : ℕ
cs₂ : List Char
step✝ : (↑final).stepIn nfa.nodes.size i (↑next) cs₂
j✝ : ℕ
cs₃ cs₄ : List Char
step : (↑final).stepIn nfa.nodes.size (↑(↑final).start) j✝ cs₃
rest : (↑final).pathIn nfa.nodes.size j✝ i cs₄
eqs : cs = cs₃ ++ cs₄ ++ cs₂
⊢ Expr.matches cs (r₁.alternate r₂)
Tactic:
cases step with
| charStep _ _ step => simp [NFA.Node.charStep, startNode] at step
| εStep _ _ step =>
  simp at eqs
  simp [NFA.Node.εStep, startNode] at step
  cases step with
  | inl eqs₁ =>
    rw [eqs₁] at rest
    have : pathToNext final next nfa.nodes.size nfa₁.val.start.val cs :=
      ⟨i, cs₄, cs₂, eqs, eq₂ ▸ rest, step⟩
    have : pathToNext nfa₁ next nfa.nodes.size nfa₁.val.start.val cs := by
      apply this.cast' nfa₁.val.start.isLt
        (Nat.le_of_lt (Nat.lt_trans nfa₂.property final.property))
        get₁
    exact .alternateLeft (ih₁ eq₁.symm this)
  | inr eqs₂ =>
    rw [eqs₂] at rest
    have : pathToNext final next nfa.nodes.size nfa₂.val.start.val cs :=
      ⟨i, cs₄, cs₂, eqs, eq₄ ▸ rest, step⟩
    have : pathToNext nfa₂ next nfa.nodes.size nfa₂.val.start.val cs := by
      apply this.cast' nfa₂.val.start.isLt (Nat.le_of_lt final.property) get₂
    have : pathToNext nfa₂ next nfa₁.val.nodes.size nfa₂.val.start.val cs := by
      apply this.castLE (ge_pushRegex_start eq₃.symm)
      intro i j h₁ h₂ step hj
      have := eq_or_ge_of_step_pushRegex eq₃.symm h₁ h₂ step
      simp at this
      cases this with
      | inl eq =>
        exfalso
        rw [eq] at hj
        exact Nat.not_le_of_gt next.isLt hj
      | inr ge => exact ge
    exact .alternateRight (ih₂ eq₃.symm this)
Proof state after:
no goals