AFTERNOON AT THE OPERA: Iolanthe. With music by Sir Arthur Sullivan and lyrics by W.S. Gilbert, a fairy tale ironically becomes a comic satire on the British House of Lords. Iolanthe, a fairy, has had an affair with the Lord Chancellor, and the result is a son, Strephon, who is half fairy and half human. He is presented with a dilemma — what will happen to his fairy half when his human half dies? After many confrontations and complications, Professor James Kolb will inform you of the solution to this conundrum. 3 p.m.