public function setSimpleMatchSets(SimpleMatchSetCollection $simpleMatchSets)
    {
        if (count($simpleMatchSets) === 2) {
            $this->simpleMatchSets = $simpleMatchSets;
        } else {
            $msg = "A MatchInteraction object must be composed of exactly two SimpleMatchSet objects.";
            throw new InvalidArgumentException($msg);
        }
    }