Task: Question Generation
Input (English):  Calchas, a soothsayer, foresees the fall of Troy and abandons the city in favour of the Greeks; his daughter, Criseyde, receives some ill will on account of her father's betrayal. Troilus, a warrior of Troy, publicly mocks love and is punished by the God of Love by being struck with irreconcilable desire for Criseyde, whom he sees passing through the temple. With the help of sly Pandarus, Criseyde's uncle, Troilus and Criseyde begin to exchange letters. Eventually, Pandarus develops a plan to urge the two into bed together; Troilus swoons when he thinks the plan is going amiss, but Pandarus and Criseyde revive him. Pandarus leaves, and Troilus and Criseyde spend a night of bliss together. Calchas eventually persuades the Greeks to exchange a prisoner of war, Antenor, for his daughter Criseyde. Hector, of Troy, objects; as does Troilus, although he does not voice his concern. Troilus speaks to Criseyde and suggests they elope but she offers a logical argument as to why it would not be practical. Criseyde promises to deceive her father and return to Troy after ten days; Troilus leaves her with a sense of foreboding. Upon arriving in the Greek camp, Criseyde realizes the unlikeliness of her being able to keep her promise to Troilus. She writes dismissively in response to his letters and on the tenth day accepts a meeting with Diomede, and listens to him speak of love. Later, she accepts him as a lover. Pandarus and Troilus wait for Criseyde: Pandarus sees that she will not return and eventually Troilus realizes this as well. Troilus curses Fortune, even more so because he still loves Criseyde; Pandarus offers some condolences. The narrator, with an apology for giving women a bad name, bids farewell to his book, and briefly recounts Troilus's death in battle and his ascent to the eighth sphere, draws a moral about the transience of earthly joys and the inadequacy of paganism, dedicates his poem to Gower and Strode, asks the protection of the Trinity, and prays that we be worthy of Christ's mercy.
Output (English): What is the name of the prisoner of war Calchas persuades the Greeks to exchange?