LOS ANGELES: Three surviving members of Led Zeppelin reunited in a California courtroom last week at a trial over whether a riff from the band's best-known song, "Stairway to Heaven," was ripped off from the founder of the band Spirit.

The copyright infringement trial resumes Tuesday in Los Angeles federal court.

Here are some things to know about the case:

RIFF RIFT

The estate of the late Randy Wolfe claims a passage from his instrumental "Taurus," was stolen by Led Zeppelin and incorporated in the opening to "Stairway," an instantly recognizable song to generations of music fans.

A riff in the 1968 "Taurus" sounds like the intro to the 1971 rock anthem. Because the copyright only applies to the sheet music filed in the Library of Congress, jurors won't hear the "Taurus" recording, only expert renditions of the sheet music.

A defense expert said the shared similarity is a descending A-minor chord progression, but that's been a musical building block for more than 300 years.

Experts for Wolfe's estate said other similarities include notes of the same duration, use of arpeggios and similar pairs of notes.

WOLFE'S SPIRIT

Wolfe, a guitar prodigy, played as a 15-year-old in Jimi Hendrix's rock group Jimmy James and the Blue Flames. Two band members were named Randy, so Hendrix dubbed him Randy California, a name he used the rest of his life.

Wolfe founded Spirit in Los Angeles in 1967 and the band played its psychedelic jazz-infused rock at "Love-Ins" during the "Summer of Love" and eventually played around the world for loyal fans.

Wolfe wrote "Taurus" for a girlfriend born under that sign of the zodiac.

A surviving band member remembered playing the song at a December 1968 Denver show, where Led Zeppelin made its U.S. debut as the opening act.

Wolfe drowned in 1997 saving his son in Hawaii.

JIMMY PAGE'S GIFT

Page, 72, a masterful guitarist who founded Led Zeppelin when The Yardbirds broke up in 1968, demonstrated a skill for deflecting questions and injecting humor in his testimony.

He said he'd never heard "Taurus" until a son-in-law showed him online comparisons to "Stairway."

"I don't do the internet," Page quipped.

He said the track was "totally alien" to him. However, he later found the album among his collection of 4,329 records and 5,882 CDs, a count he said was "as of yesterday."

Asked if he was a gifted guitarist, Page paused for a long moment and said, "Well, yeah." The courtroom erupted with laughter.

Page carried a guitar into court, but left without playing a note — unless you count a spontaneous air guitar solo during a break with singer Robert Plant.

FLEXIBLE STATUTE FOR IMITATIONS

While it seems late to bring a case against a 45-year-old song, copyright lawsuits can be filed if rights were allegedly violated in the past three years.

And damages can only extend back three years and into the future.

The lawsuit was filed in 2014, so damages could be awarded from 2011 onward.

A financial expert for the estate said Led Zeppelin works that include "Stairway" raked in nearly $60 million in the past five years.

The defense, which denies any plagiarism, is trying to show that even if the copyright was infringed, it was only a short portion of an epic song famous for its lyrics and crescendo-building momentum.

RIPOFF REMIX

Led Zeppelin has been down this track before — several times.

The band has reached at least six settlements over songwriting credits for some of their best-known works, including "Whole Lotta Love," ''The Lemon Song," and "Dazed and Confused," according to the lawsuit.

The judge, however, barred the jury from hearing evidence of those settlements after the defense argued it was irrelevant and would tar Page and Plant "as serial copiers."

Bass player and keyboardist John Paul Jones, who testified briefly on Friday, has been dismissed as a defendant.