Duration of copyright is one way it was perverted, but the other direction was scope. In 1930 judge Hand said in relation to Nichols v. Universal Pictures:

> Upon any work...a great number of patterns of increasing generality will fit equally well. At the one end is the most concrete possible expression...at the other, a title...Nobody has ever been able to fix that boundary, and nobody ever can...As respects play, plagiarism may be found in the 'sequence of events'...this trivial points of expression come to be included.

And since then a litany of judges and tests expanded the notion of infringement towards vibes and away from expression:

- Hand's Abstractions / The "Patterns" Test (Nichols v. Universal Pictures)

- Total Concept and Feel (Roth Greeting Cards v. United Card Co.)

- The Krofft Test / Extrinsic and Intrinsic Analysis

- Sequence, Structure, and Organization (Whelan Associates v. Jaslow Dental Laboratory)

- Abstraction-Filtration-Comparison (AFC) Test (Computer Associates v. Altai)

The trend has been to make infringement more and more abstract over time, but this makes testing it an impossible burden. How do you ensure you are not infringing any protected abstraction on any level in any prior work? Due diligence has become too difficult now.