Object2IntMap<GrVariable> (@NotNull List<? extends Object2IntMap<GrVariable>> ins) { if (ins.isEmpty()) { return NEUTRAL; } if (ins.size() == 1) { return ins.get(0); } final Object2IntMap<GrVariable> result = new Object2IntOpenHashMap<>(); for (Object2IntMap<GrVariable> i : ins) { merge(result, i); } return result; }