expr_fvs (Cast expr co) fv_cand in_scope acc =
  (expr_fvs expr `unionFV` tyCoFVsOfCo co) fv_cand in_scope acc
expr_fvs (Cast expr co) fv_cand in_scope acc =
  (expr_fvs expr `unionFV` tyCoFVsOfCo co) fv_cand in_scope acc
expr_fvs (Cast expr co) fv_cand in_scope acc =
  (expr_fvs expr `unionFV` tyCoFVsOfCo co) fv_cand in_scope acc