Here's a bit of rock trivia to start your week: What is the only band whose core members each have been inducted twice into the Rock and Roll Hall of Fame? (Hint – it's not the Beatles.)

Give yourself a pat on the iPod if you said CSNY. That is, Crosby, Stills, Nash and Young ... three of whom (all but Neil Young) were in concert Sunday night at the Riverside Theater.

This was the Milwaukee stop on the 2012 tour of David Crosby, Stephen Stills and Graham Nash, whose tight harmonies, delicate melodies and insightful lyrics created a new branch to the folk rock tree in the late 1960s.

In the beginning, there was The Byrds, which begat Crosby; Buffalo Springfield, which begat Stills; and The Hollies, which begat Nash. While the three were acquainted, it was a 1968 party at the home of Mama Cass Elliot where the magic began when Nash added an impromptu second harmony to a Crosby/Stills duet and the eureka moment occurred.

There was – and is – something special in the air when those three voices come together.

From the opening "CarryOn/Questions" through their encore of "Suite Judy Blue Eyes," CSN had the full house on its feet. The evening explored the full range of their musical gifts, from the tender "Our House" and "Helplessly Hoping" to the bluesy "Southern Cross" and the full-bore rock 'n' roll of "Marrakesh Express" and "Almost Cut My Hair."

One could be forgiven for assuming that two septuagenarians (Crosby is on the cusp of 71 and Nash is 70) and the 67-year-old Stills would pace themselves for 90 minutes or so and call it a good night. Not so. They gave us full measure for nearly three hours and two dozen songs.

There have been several permutations of CSNY over the years, both in the studio and on tour. We recall seeing an acoustic C&N at this venue a few years ago and wishing for a bit of Stills to season the offering. Wish fulfilled as his extraordinary guitar play returned the trio to full voice.

The last 45 years have not been easy on D…