This is a very tight area of the business.It is a very different thging to have such an appreciation of a fellow artist that on your own tune you place a bit of their inspiration upon it.Their also are allowances and serious limitations upon that,you can go on as long as you want yet after a certain number of measures you have got to give a co-writer credit.We work you see from our influences,that can't be helped.For the chicago blues musicians it was a flattery for one guy to do another's licks.yet this was not the white guy big money rock and roll world,all of these cats were just doing clubs around the area and that was as big as they thought at the time it was ever going to get.They were not getting paid royalties by their labels and it was all the beginning of something.And it got really big when a bunch of young english kids began to pick up on what america did not notice.Especially The Rolling Stones who were searching for the most obscure chicago blues that they could cover and they credited and paid the songwriters.And when at last they began to write it waS totally original to them,yes some borrowed riffs and this and that but it does not matter as long as the original idea is your stuff.They screwed up pretty bad on this with "Love In Vain" credited to Woody Payne but it was all Robert Johnson and they did not think that anyone in America would ever know who Robert Johnson was at that time.And many American's would not ever have discovered Robert Johnson if the stones had not tried to lift from him without appropriate credit.Not nuances and textures mind you,the whole fucking song!Led Zepplin if you only knew,ripped off everyone they could in their time.Shamelessly so,had to settle many lawsuits out of court to avoid the bad publicity.They would openly take a Muddy Waters,Willie Dixon,or Howlin wolf number and credit it all to Page/Plant/Jones/Bonham and when your album sales are 5 million plus that is a lot of money that you are not paying in due royalties.The most famous song they did "Stairway to Heaven" came from an intro riff from a band they warmed up for in 1968,Spirit featuring Randy California and the song was "Taurus"a direct and complete rip-off.Oh man reallly bad.They never acknowleged it,never thanked him nor paid him a penny.They just stole it and called it their own.Probably they will one day deal with a massive and serious lawsuit over this from Randy's estate.Randy spoke about it before he died "I would have thought that at least they would have called to thank me."This kind of a process in the world of rock and roll,it is okay to take someone else's idea and expand on it and make it your own,but you have to give credit to the original author of it and pay up royalties.They all knew it,Jimmy Page most certainly knew it as randy taught him how to play it.And all of that is okay,one artist inspires another yet you have got to give credit to them and you must pay the due royalties for it.