class MemoryStore:
    def __init__(self):
        self.records = {}
        self.score_history = {}

    def store(self, agent, expr, score):
        if agent not in self.records or self.records[agent]['score'] < score:
            self.records[agent] = {'expression': expr, 'score': score}
        if agent not in self.score_history:
            self.score_history[agent] = []
        self.score_history[agent].append(score)

    def get(self, agent):
        return self.records.get(agent, None)