{motive : Mathlib.Tactic.Translate.CastKind✝ → Sort u} →
  (t : Mathlib.Tactic.Translate.CastKind✝¹) →
    Mathlib.Tactic.Translate.CastKind.ctorIdx✝ t = 1 → motive Mathlib.Tactic.Translate.CastKind.unfoldFun✝ → motive t