Lacan goes to a wedding but persistently mistakes a bridesmaid for the bride, repeatedly interrupts the bride’s father’s speech, and insists on giving a rambling, self-aggrandising speech of his own. It is then discovered that he is at the wrong wedding and nobody knows who he is.
Badiou is summoned to a meeting with Lacan, who agonisingly slowly and in total silence draws on a piece of paper a Venn diagram labelled with Greek letters. Finally, Lacan holds up the paper in front of Badiou’s face and punches a hole in it with his pencil, stabbing Badiou in the forehead. Badiou, enlightened, departs without a word.
Lacan and Derrida discover they have been sharing the same mistress, each under the mistaken impression that the other (whom he never encounters directly) is her husband - one enters by the door as the other leaves by the window. After the subterfuge is discovered, they continue in this arrangement for several months.