But then there are the aftereffects...

The song’s not quite the same, but the opening of “Stairway to Heaven” is close enough to an obscure 1960s album track to warrant a trial that might rewrite the history of rock ’n’roll over a song-writing credit.
Led Zeppelin founders Jimmy Page, 72, and Robert Plant, 67, are expected to recount the origins of the song more than 40 years ago at a trial scheduled to start May 10 in Los Angeles. Lawyers for the two rockers have asked the judge to exclude evidence of the “adverse effects of drinking or drug use in the 1960s or later” as a factor in their allegedly flawed recollection of whether they were familiar with a song they are accused of copying.