-- Mathlib/Data/Ordmap/Ordset.lean
theorem balance_eq_balance' {l x r} (hl : Balanced l) (hr : Balanced r) (sl : Sized l)
    (sr : Sized r) : @balance α l x r = balance' l x r

Proof state:
case nil.node.node.node
α : Type u_1
x : α
hl : nil.Balanced
sl : nil.Sized
rs : ℕ
rx : α
rls : ℕ
rll : Ordnode α
rlx : α
rlr : Ordnode α
rrs : ℕ
rrl : Ordnode α
rrx : α
rrr : Ordnode α
hr : ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr)).Balanced
sr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Sized
⊢ (if 0 + (rls + rrs + 1) ≤ 1 then nil.node' x ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr))
    else
      if rls + rrs + 1 > 0 then nil.rotateL x ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr))
      else nil.node' x ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr))) =
    if rls < ratio * rrs then
      node (rls + rrs + 1 + 1) (node (rls + 1) nil x (node rls rll rlx rlr)) rx (node rrs rrl rrx rrr)
    else
      node (rls + rrs + 1 + 1) (node (rll.size + 1) nil x rll) rlx
        (node (rlr.size + rrs + 1) rlr rx (node rrs rrl rrx rrr))

Tactic:
rw [zero_add, if_neg, if_pos, rotateL]

Result:
case nil.node.node.node
α : Type u_1
x : α
hl : nil.Balanced
sl : nil.Sized
rs : ℕ
rx : α
rls : ℕ
rll : Ordnode α
rlx : α
rlr : Ordnode α
rrs : ℕ
rrl : Ordnode α
rrx : α
rrr : Ordnode α
hr : ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr)).Balanced
sr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Sized
⊢ (if (node rls rll rlx rlr).size < ratio * (node rrs rrl rrx rrr).size then
      nil.node3L x (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)
    else nil.node4L x (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)) =
    if rls < ratio * rrs then
      node (rls + rrs + 1 + 1) (node (rls + 1) nil x (node rls rll rlx rlr)) rx (node rrs rrl rrx rrr)
    else
      node (rls + rrs + 1 + 1) (node (rll.size + 1) nil x rll) rlx
        (node (rlr.size + rrs + 1) rlr rx (node rrs rrl rrx rrr))

case nil.node.node.node.hc
α : Type u_1
x : α
hl : nil.Balanced
sl : nil.Sized
rs : ℕ
rx : α
rls : ℕ
rll : Ordnode α
rlx : α
rlr : Ordnode α
rrs : ℕ
rrl : Ordnode α
rrx : α
rrr : Ordnode α
hr : ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr)).Balanced
sr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Sized
⊢ rls + rrs + 1 > 0

case nil.node.node.node.hnc
α : Type u_1
x : α
hl : nil.Balanced
sl : nil.Sized
rs : ℕ
rx : α
rls : ℕ
rll : Ordnode α
rlx : α
rlr : Ordnode α
rrs : ℕ
rrl : Ordnode α
rrx : α
rrr : Ordnode α
hr : ((node rls rll rlx rlr).node' rx (node rrs rrl rrx rrr)).Balanced
sr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Sized
⊢ ¬rls + rrs + 1 ≤ 1

Proof state:
case neg
α : Type u_1
x : α
ls : ℕ
lx : α
rs : ℕ
rl : Ordnode α
rx : α
rr : Ordnode α
hr : (node rs rl rx rr).Balanced
sr : (node rs rl rx rr).Sized
h : ¬delta * ls < rs
h_1 : delta * rs < ls
lls : ℕ
lll : Ordnode α
llx : α
llr : Ordnode α
lrs : ℕ
lrl : Ordnode α
lrx : α
lrr : Ordnode α
hl : (node ls (node lls lll llx llr) lx (node lrs lrl lrx lrr)).Balanced
sl : (node ls (node lls lll llx llr) lx (node lrs lrl lrx lrr)).Sized
ld : delta ≤ (node lls lll llx llr).size + (node lrs lrl lrx lrr).size
h✝ : ¬lrs < ratio * lls
⊢ lls + lrl.size + 1 + (lrr.size + rs + 1) = lls + (lrl.size + lrr.size + 1) + 1 + rs

Tactic:
abel

Result:
no goals

Proof state:
case pos
α : Type u_1
x : α
ls : ℕ
ll : Ordnode α
lx : α
lr : Ordnode α
hl : (node ls ll lx lr).Balanced
sl : (node ls ll lx lr).Sized
rs : ℕ
rx : α
h : delta * ls < rs
rls : ℕ
rll : Ordnode α
rlx : α
rlr : Ordnode α
rrs : ℕ
rrl : Ordnode α
rrx : α
rrr : Ordnode α
hr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Balanced
sr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Sized
rd : delta ≤ (node rls rll rlx rlr).size + (node rrs rrl rrx rrr).size
h✝ : rls < ratio * rrs
⊢ (node ls ll lx lr).node3L x (node rls rll rlx rlr) rx (node rrs rrl rrx rrr) =
    node (ls + rs + 1) (node (ls + rls + 1) (node ls ll lx lr) x (node rls rll rlx rlr)) rx (node rrs rrl rrx rrr)

Tactic:
simp [node3L, node', sr.1]

Result:
case pos
α : Type u_1
x : α
ls : ℕ
ll : Ordnode α
lx : α
lr : Ordnode α
hl : (node ls ll lx lr).Balanced
sl : (node ls ll lx lr).Sized
rs : ℕ
rx : α
h : delta * ls < rs
rls : ℕ
rll : Ordnode α
rlx : α
rlr : Ordnode α
rrs : ℕ
rrl : Ordnode α
rrx : α
rrr : Ordnode α
hr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Balanced
sr : (node rs (node rls rll rlx rlr) rx (node rrs rrl rrx rrr)).Sized
rd : delta ≤ (node rls rll rlx rlr).size + (node rrs rrl rrx rrr).size
h✝ : rls < ratio * rrs
⊢ ls + rls + 1 + rrs = ls + (rls + rrs + 1)

Proof state:
case pos
α : Type u_1
x : α
ls : ℕ
ll : Ordnode α
lx : α
lr : Ordnode α
hl : (node ls ll lx lr).Balanced
sl : (node ls ll lx lr).Sized
rs : ℕ
rl : Ordnode α
rx : α
rr : Ordnode α
hr : (node rs rl rx rr).Balanced
sr : (node rs rl rx rr).Sized
h : delta * ls < rs
⊢ (node ls ll lx lr).rotateL x (node rs rl rx rr) =
    rec nil
      (fun size l x_1 r l_ih r_ih =>
        rec nil
          (fun size_1 l_1 x_2 r_1 l_ih r_ih =>
            if size < ratio * size_1 then node (ls + rs + 1) (node (ls + size + 1) (node ls ll lx lr) x rl) rx rr
            else
              node (ls + rs + 1) (node (ls + l.size + 1) (node ls ll lx lr) x l) x_1
                (node (r.size + size_1 + 1) r rx rr))
          rr)
      rl

Tactic:
have rd : delta ≤ size rl + size rr := by
  have := lt_of_le_of_lt (Nat.mul_le_mul_left _ sl.pos) h
  rwa [sr.1, Nat.lt_succ_iff] at this

Result:
case pos
α : Type u_1
x : α
ls : ℕ
ll : Ordnode α
lx : α
lr : Ordnode α
hl : (node ls ll lx lr).Balanced
sl : (node ls ll lx lr).Sized
rs : ℕ
rl : Ordnode α
rx : α
rr : Ordnode α
hr : (node rs rl rx rr).Balanced
sr : (node rs rl rx rr).Sized
h : delta * ls < rs
rd : delta ≤ rl.size + rr.size
⊢ (node ls ll lx lr).rotateL x (node rs rl rx rr) =
    rec nil
      (fun size l x_1 r l_ih r_ih =>
        rec nil
          (fun size_1 l_1 x_2 r_1 l_ih r_ih =>
            if size < ratio * size_1 then node (ls + rs + 1) (node (ls + size + 1) (node ls ll lx lr) x rl) rx rr
            else
              node (ls + rs + 1) (node (ls + l.size + 1) (node ls ll lx lr) x l) x_1
                (node (r.size + size_1 + 1) r rx rr))
          rr)
      rl

Proof state:
case node.nil.node.node
α : Type u_1
x : α
ls : ℕ
lx : α
hr : nil.Balanced
sr : nil.Sized
lls : ℕ
lll : Ordnode α
llx : α
llr : Ordnode α
lrs : ℕ
lrl : Ordnode α
lrx : α
lrr : Ordnode α
hl : ((node lls lll llx llr).node' lx (node lrs lrl lrx lrr)).Balanced
sl : (node ls (node lls lll llx llr) lx (node lrs lrl lrx lrr)).Sized
⊢ (if (node lrs lrl lrx lrr).size < ratio * (node lls lll llx llr).size then
      (node lls lll llx llr).node3R lx (node lrs lrl lrx lrr) x nil
    else (node lls lll llx llr).node4R lx (node lrs lrl lrx lrr) x nil) =
    if lrs < ratio * lls then
      node (lls + lrs + 1 + 1) (node lls lll llx llr) lx (node (lrs + 1) (node lrs lrl lrx lrr) x nil)
    else
      node (lls + lrs + 1 + 1) (node (lls + lrl.size + 1) (node lls lll llx llr) lx lrl) lrx
        (node (lrr.size + 1) lrr x nil)

Tactic:
dsimp only [size_node]

Result:
case node.nil.node.node
α : Type u_1
x : α
ls : ℕ
lx : α
hr : nil.Balanced
sr : nil.Sized
lls : ℕ
lll : Ordnode α
llx : α
llr : Ordnode α
lrs : ℕ
lrl : Ordnode α
lrx : α
lrr : Ordnode α
hl : ((node lls lll llx llr).node' lx (node lrs lrl lrx lrr)).Balanced
sl : (node ls (node lls lll llx llr) lx (node lrs lrl lrx lrr)).Sized
⊢ (if lrs < ratio * lls then (node lls lll llx llr).node3R lx (node lrs lrl lrx lrr) x nil
    else (node lls lll llx llr).node4R lx (node lrs lrl lrx lrr) x nil) =
    if lrs < ratio * lls then
      node (lls + lrs + 1 + 1) (node lls lll llx llr) lx (node (lrs + 1) (node lrs lrl lrx lrr) x nil)
    else
      node (lls + lrs + 1 + 1) (node (lls + lrl.size + 1) (node lls lll llx llr) lx lrl) lrx
        (node (lrr.size + 1) lrr x nil)