∀ {α : Type u} {β : α → Type v} {k : α} {v : β k} {l r : Std.DTreeMap.Internal.Impl α β} {hlb : l.Balanced}
  {hrb : r.Balanced} {hlr : Std.DTreeMap.Internal.Impl.BalanceLErasePrecond l.size r.size},
  Std.DTreeMap.Internal.Impl.balanceLErase k v l r hlb hrb hlr = Std.DTreeMap.Internal.Impl.balance k v l r hlb hrb ⋯