α : Type u_1
l : Ordnode α
x : α
m : Ordnode α
y : α
r : Ordnode α
⊢ (((match l with
            | nil => 0
            | node sz l x r => sz) +
            match m with
            | nil => 0
            | node sz l x r => sz) +
          1 +
        match r with
        | nil => 0
        | node sz l x r => sz) +
      1 =
    (((match l with
          | nil => 0
          | node sz l x r => sz) +
          match m with
          | nil => 0
          | node sz l x r => sz) +
        match r with
        | nil => 0
        | node sz l x r => sz) +
      2
α : Type u_1
l : Ordnode α
x : α
m : Ordnode α
y : α
r : Ordnode α
⊢ size (node3L l x m y r) = size l + size m + size r + 2
dsimp [node3L, node', size]
no goals
α : Type u_1
l : Ordnode α
x : α
m : Ordnode α
y : α
r : Ordnode α
⊢ (((match l with
            | nil => 0
            | node sz l x r => sz) +
            match m with
            | nil => 0
            | node sz l x r => sz) +
          1 +
        match r with
        | nil => 0
        | node sz l x r => sz) +
      1 =
    (((match l with
          | nil => 0
          | node sz l x r => sz) +
          match m with
          | nil => 0
          | node sz l x r => sz) +
        match r with
        | nil => 0
        | node sz l x r => sz) +
      2
rw [add_right_comm _ 1]