let empty_acc =
  let a = { p_hyp = []; p_goal = []; p_both = []; p_cut = [];
    call_hyp = []; call_pre = []; a_call = WpPropId.empty_assigns_info;
    a_goal = WpPropId.empty_assigns_info; a_hyp = WpPropId.empty_assigns_info; }
  in { has_asgn_goal = false; has_prop_goal = false; info = a; }