Sometimes you want to read some seminal paper from the 70s (somehow, most of the seminal papers are from the seventies), and half of the time it's re-hosted by

Sometimes you want to read some seminal paper from the 70s (somehow, most of the seminal papers are from the seventies), and half of the time it's re-hosted by someone or some university and is freely available, but another half of the time, all you have is an acm.org or citeseer page without the "Download PDF" link. Now what? This stuff is 40 years old, by all rights it should be public domain by now.