def get_places_with_missing_tokens(t, marking):
    """
    Get places with missing tokens

    Parameters
    ----------
    t
        Transition to enable
    marking
        Current marking
    """
    places_with_missing = set()
    for a in t.in_arcs:
        if marking[a.source] < a.weight:
            places_with_missing.add(a.source)
    return places_with_missing
