Theorem: CompositionSeries.Equivalent.smash
File: Mathlib/Order/JordanHolder.lean

Proof steps:
state_before: X : Type u
inst✝¹ : Lattice X
inst✝ : JordanHolderLattice X
s₁ s₂ t₁ t₂ : CompositionSeries X
hs : last s₁ = head s₂
ht : last t₁ = head t₂
h₁ : s₁.Equivalent t₁
h₂ : s₂.Equivalent t₂
e : Fin (s₁.length + s₂.length) ≃ Fin (t₁.length + t₂.length) :=
  Trans.trans (Trans.trans finSumFinEquiv.symm ((Exists.choose h₁).sumCongr (Exists.choose h₂))) finSumFinEquiv
⊢ ∀ (i : Fin (smash s₁ s₂ hs).length),
    Iso ((smash s₁ s₂ hs).toFun i.castSucc, (smash s₁ s₂ hs).toFun i.succ)
      ((smash t₁ t₂ ht).toFun (e i).castSucc, (smash t₁ t₂ ht).toFun (e i).succ)
state_after: X : Type u
inst✝¹ : Lattice X
inst✝ : JordanHolderLattice X
s₁ s₂ t₁ t₂ : CompositionSeries X
hs : last s₁ = head s₂
ht : last t₁ = head t₂
h₁ : s₁.Equivalent t₁
h₂ : s₂.Equivalent t₂
e : Fin (s₁.length + s₂.length) ≃ Fin (t₁.length + t₂.length) :=
  Trans.trans (Trans.trans finSumFinEquiv.symm ((Exists.choose h₁).sumCongr (Exists.choose h₂))) finSumFinEquiv
i : Fin (smash s₁ s₂ hs).length
⊢ Iso ((smash s₁ s₂ hs).toFun i.castSucc, (smash s₁ s₂ hs).toFun i.succ)
    ((smash t₁ t₂ ht).toFun (e i).castSucc, (smash t₁ t₂ ht).toFun (e i).succ)
tactic: intro i
state_before: X : Type u
inst✝¹ : Lattice X
inst✝ : JordanHolderLattice X
s₁ s₂ t₁ t₂ : CompositionSeries X
hs : last s₁ = head s₂
ht : last t₁ = head t₂
h₁ : s₁.Equivalent t₁
h₂ : s₂.Equivalent t₂
e : Fin (s₁.length + s₂.length) ≃ Fin (t₁.length + t₂.length) :=
  Trans.trans (Trans.trans finSumFinEquiv.symm ((Exists.choose h₁).sumCongr (Exists.choose h₂))) finSumFinEquiv
i : Fin (smash s₁ s₂ hs).length
⊢ Iso ((smash s₁ s₂ hs).toFun i.castSucc, (smash s₁ s₂ hs).toFun i.succ)
    ((smash t₁ t₂ ht).toFun (e i).castSucc, (smash t₁ t₂ ht).toFun (e i).succ)
state_after: case refine_1
X : Type u
inst✝¹ : Lattice X
inst✝ : JordanHolderLattice X
s₁ s₂ t₁ t₂ : CompositionSeries X
hs : last s₁ = head s₂
ht : last t₁ = head t₂
h₁ : s₁.Equivalent t₁
h₂ : s₂.Equivalent t₂
e : Fin (s₁.length + s₂.length) ≃ Fin (t₁.length + t₂.length) :=
  Trans.trans (Trans.trans finSumFinEquiv.symm ((Exists.choose h₁).sumCongr (Exists.choose h₂))) finSumFinEquiv
i : Fin (smash s₁ s₂ hs).length
⊢ ∀ (i : Fin s₁.length),
    Iso
      ((smash s₁ s₂ hs).toFun (Fin.castAdd s₂.length i).castSucc, (smash s₁ s₂ hs).toFun (Fin.castAdd s₂.length i).succ)
      ((smash t₁ t₂ ht).toFun (e (Fin.castAdd s₂.length i)).castSucc,
        (smash t₁ t₂ ht).toFun (e (Fin.castAdd s₂.length i)).succ)

case refine_2
X : Type u
inst✝¹ : Lattice X
inst✝ : JordanHolderLattice X
s₁ s₂ t₁ t₂ : CompositionSeries X
hs : last s₁ = head s₂
ht : last t₁ = head t₂
h₁ : s₁.Equivalent t₁
h₂ : s₂.Equivalent t₂
e : Fin (s₁.length + s₂.length) ≃ Fin (t₁.length + t₂.length) :=
  Trans.trans (Trans.trans finSumFinEquiv.symm ((Exists.choose h₁).sumCongr (Exists.choose h₂))) finSumFinEquiv
i : Fin (smash s₁ s₂ hs).length
⊢ ∀ (i : Fin s₂.length),
    Iso ((smash s₁ s₂ hs).toFun (Fin.natAdd s₁.length i).castSucc, (smash s₁ s₂ hs).toFun (Fin.natAdd s₁.length i).succ)
      ((smash t₁ t₂ ht).toFun (e (Fin.natAdd s₁.length i)).castSucc,
        (smash t₁ t₂ ht).toFun (e (Fin.natAdd s₁.length i)).succ)
tactic: refine Fin.addCases ?_ ?_ i