Module: Mathlib.Data.Ordmap.Invariants

Goal state before:
pp: case pos
α : Type u_1
x : α
rs : ℕ
rl : Ordnode α
rx : α
rr : Ordnode α
ls : ℕ
ll : Ordnode α
lx : α
lr : Ordnode α
h✝ : ls > delta * rs
⊢ (rec nil
        (fun size l x_1 r l_ih r_ih ↦
          rec nil
            (fun size_1 l x_2 r l_ih r_ih ↦
              if size_1 < ratio * size then node (ls + rs + 1) ll lx (node (rs + size_1 + 1) lr x (node rs rl rx rr))
              else
                node (ls + rs + 1) (node (size + l.size + 1) ll lx l) x_2
                  (node (r.size + rs + 1) r x (node rs rl rx rr)))
            lr)
        ll).dual =
    rec nil
      (fun size l x_1 r l_ih r_ih ↦
        rec nil
          (fun size_1 l x_2 r l_ih r_ih ↦
            if size_1 < ratio * size then
              node (rs + ls + 1) (node (rs + size_1 + 1) (node rs rr.dual rx rl.dual) x lr.dual) lx ll.dual
            else
              node (rs + ls + 1) (node (rs + l.size + 1) (node rs rr.dual rx rl.dual) x l) x_2
                (node (r.size + size + 1) r lx ll.dual))
          lr.dual)
      ll.dual

Tactic:
obtain - | ⟨lls, lll, llx, llr⟩ := ll

Goal state after:
case pos.nil
α : Type u_1
x : α
rs : ℕ
rl : Ordnode α
rx : α
rr : Ordnode α
ls : ℕ
lx : α
lr : Ordnode α
h✝ : ls > delta * rs
⊢ (rec nil
        (fun size l x_1 r l_ih r_ih ↦
          rec nil
            (fun size_1 l x_2 r l_ih r_ih ↦
              if size_1 < ratio * size then node (ls + rs + 1) nil lx (node (rs + size_1 + 1) lr x (node rs rl rx rr))
              else
                node (ls + rs + 1) (node (size + l.size + 1) nil lx l) x_2
                  (node (r.size + rs + 1) r x (node rs rl rx rr)))
            lr)
        nil).dual =
    rec nil
      (fun size l x_1 r l_ih r_ih ↦
        rec nil
          (fun size_1 l x_2 r l_ih r_ih ↦
            if size_1 < ratio * size then
              node (rs + ls + 1) (node (rs + size_1 + 1) (node rs rr.dual rx rl.dual) x lr.dual) lx nil.dual
            else
              node (rs + ls + 1) (node (rs + l.size + 1) (node rs rr.dual rx rl.dual) x l) x_2
                (node (r.size + size + 1) r lx nil.dual))
          lr.dual)
      nil.dual

case pos.node
α : Type u_1
x : α
rs : ℕ
rl : Ordnode α
rx : α
rr : Ordnode α
ls : ℕ
lx : α
lr : Ordnode α
h✝ : ls > delta * rs
lls : ℕ
lll : Ordnode α
llx : α
llr : Ordnode α
⊢ (rec nil
        (fun size l x_1 r l_ih r_ih ↦
          rec nil
            (fun size_1 l x_2 r l_ih r_ih ↦
              if size_1 < ratio * size then
                node (ls + rs + 1) (node lls lll llx llr) lx (node (rs + size_1 + 1) lr x (node rs rl rx rr))
              else
                node (ls + rs + 1) (node (size + l.size + 1) (node lls lll llx llr) lx l) x_2
                  (node (r.size + rs + 1) r x (node rs rl rx rr)))
            lr)
        (node lls lll llx llr)).dual =
    rec nil
      (fun size l x_1 r l_ih r_ih ↦
        rec nil
          (fun size_1 l x_2 r l_ih r_ih ↦
            if size_1 < ratio * size then
              node (rs + ls + 1) (node (rs + size_1 + 1) (node rs rr.dual rx rl.dual) x lr.dual) lx
                (node lls lll llx llr).dual
            else
              node (rs + ls + 1) (node (rs + l.size + 1) (node rs rr.dual rx rl.dual) x l) x_2
                (node (r.size + size + 1) r lx (node lls lll llx llr).dual))
          lr.dual)
      (node lls lll llx llr).dual