A more thorough explanation:

The Abstraction-Filtration-Comparison Test is a legal test used to determine whether two works are substantially similar in an infringement case. It was created by the courts and involves three steps:

1. Abstraction Test: The court breaks down the copyrighted work into its different levels of abstraction or generality.
2. Filtration Test: The court examines each level of abstraction and removes any unprotectable elements such as ideas, processes, facts, public-domain information, and merger material.
3. Comparison Test: The court compares the remaining core of protectable expression with the accused work to determine if there has been any misappropriation of substantial elements of the copyrighted work.

The Abstraction-Filtration-Comparison Test was first used in a case involving computer software, but it has since been applied to other types of works as well.

Suppose a musician creates a song and copyrights it. Another musician later creates a song that sounds very similar to the first song. The first musician could use the Abstraction-Filtration-Comparison Test to determine if the second song infringes on their copyright.

1. Abstraction Test: The court breaks down the structure of the first song into its different levels of abstraction, such as melody, harmony, and lyrics.
2. Filtration Test: The court examines each level of abstraction and removes any unprotectable elements, such as common chord progressions or basic song structures.
3. Comparison Test: The court compares the remaining core of protectable expression with the second song to determine if there has been any misappropriation of substantial elements of the first song.

If the court finds that the second song has copied substantial elements of the first song's protectable expression, then it may be considered an infringement of the first musician's copyright.