@Override
    protected void begin(UniqueOperation op, OperationTree node) {
      super.begin(op, node);

      for (OperationTree root : allOperations(op)) root.findAll(UniqueOperation.class, out);

      for (UniqueOperation operation : out) {
        if (operation != op && op.tag.equals(operation.tag)) operation.completed = true;
      }

      out.clear();
    }
    @Override
    protected float act(float delta, UniqueOperation op, OperationTree node) {
      if (op.completed) // avoid processing the tick it was
      return delta; // invalidated by another unique

      OperationTree wrapped = node.children().get(0);
      delta = wrapped.act(delta);
      op.completed = wrapped.isComplete();

      return delta;
    }