public void markAttached() {
        this.unattached = false;
    }

    public boolean isUnattached() {
        return unattached;
    }

    void markUsed() {
        this.used = true;
    }

    void markUnused() {
        this.used = false;
    }

    /**
     * Indicates whether the edge is currently listed as outgoing in a node.