when:
        addNode(node1)

        then:
        bindings.getRulesWithInput(nodeAtState("a", ModelNode.State.Finalized)) as List == [rule]
        rule.inputBindings[0].boundTo == node1

        when:
        removeNode(node1)

        then:
        bindings.getRulesWithInput(nodeAtState("a", ModelNode.State.Finalized)) as List == []
        !rule.subjectBinding.bound

        return rulesBySubject.get(target);
    }

    /**
     * Returns the set of rules with the given input.
     */
    public Collection<RuleBinder> getRulesWithInput(NodeAtState input) {
        return rulesByInput.get(input);
    }

    private static class Reference {
        final ModelBinding binding;
        final NodeAtStateIndex index;

            this.input = input;
        }

        @Override
        public boolean calculateDependencies(GoalGraph graph, Collection<ModelGoal> dependencies) {
            for (RuleBinder rule : ruleBindings.getRulesWithInput(input)) {
                ModelBinding subjectBinding = rule.getSubjectBinding();
                if (!subjectBinding.isBound()) {
                    // TODO - implement these cases
                    continue;