When we were growing up, the 45 single was the heart of rock-and-roll and in many regards still is. It's the hardest thing to pull off. The surest sign that a band is growing stale and running out of creative ideas is when it turns to prog. And I well remember the 1970s when prog almost destroyed rock music. It's the mold growing on a congealed band on its last legs. Indeed, it still lurks among us in new, insidious forms like indie. The few times U2 has attempted prog, we've tempered it with good songwriting.