{motive : Lean.Elab.Tactic.Grind.SimpCacheKey → Sort u} →
  ((variant : Lean.Name) →
      (extras : Array Lean.Elab.Tactic.Grind.ExtraTheorem) → motive { variant := variant, extras := extras }) →
    (t : Lean.Elab.Tactic.Grind.SimpCacheKey) → motive t