∀ {o : Ordinal.{max u_1 u_2}} {f : (a : Ordinal.{max u_1 u_2}) → a < o → Ordinal.{max u_1 u_2}}
  {c : Cardinal.{max u_1 u_2}},
  c.IsRegular → o.card < c → (∀ (i : Ordinal.{max u_1 u_2}) (hi : i < o), f i hi < c.ord) → o.blsub f < c.ord