{motive_2 : Lean.IR.FnBody → Sort u} →
  (t : Lean.IR.FnBody) →
    t.ctorIdx = 0 →
      ((x : Lean.IR.VarId) →
          (ty : Lean.IR.IRType) →
            (e : Lean.IR.Expr) → (b : Lean.IR.FnBody) → motive_2 (Lean.IR.FnBody.vdecl x ty e b)) →
        motive_2 t