public function insert(RuleWatchNode $node)
    {
        if ($node->getRule()->isAssertion()) {
            return;
        }

        foreach (array($node->watch1, $node->watch2) as $literal) {
            if (!isset($this->watchChains[$literal])) {
                $this->watchChains[$literal] = new RuleWatchChain;
            }

            $this->watchChains[$literal]->unshift($node);
        }
    }