Seinfeld/Mad About You Crossovers

If you reject mere actor crossovers than that would leave only two instances in which Seinfeld characters(not just the actors who played the parts) crossed over. The two being the Mad About You episode in which we find Paul Buchman is subletting his old batchelor pad to Kramer and the Mad About You episode in which Paul and his cousin Ira encounter Jerry Seinfeld on the streets of New York city.