anchor.diff:  check_gexpr([Fun|As], Env, L, St0) when is_atom(Fun) ->
       St1 = check_gargs(As, Env, L, St0),
       %% Function must be a legal guard bif AND not a defined function.
  -    case is_gbound(Fun, safe_length(As), Env) of
  +    case lfe_env:is_gbound(Fun, safe_length(As), Env) of
           true -> St1;
           false -> illegal_guard_error(L, St1)
       end;
  
positive.code: pat_bit_size(N, _, _, _, _, _, St) when is_integer(N), N > 0 -> St;
  pat_bit_size(S, _, Bvs, _, Env, L, St) when is_atom(S) ->
      %% Size must be bound here or occur earlier in binary pattern.
      case is_element(S, Bvs) or is_vbound(S, Env) of
          true -> St;
          false -> add_error(L, {unbound_symb,S}, St)
      end;
  
negative.code: %%  Check if Func/Arity is bound.
  
  check_func(F, Ar, Env, L, St) ->
      case lfe_env:is_fbound(F, Ar, Env) of
          true -> St;
          false -> unbound_func_error(L, {F,Ar}, St)
      end.
  