Jag läser en bok

Jag läser the Princeton companion to mathematics, och där står:

What does it mean to say that The Companion is “arrangedthematically”?Theansweristhatitisdivided into eight parts, each with a different general theme and a different purpose. Part I consists of introductory material, which gives a broad overview of mathematics and explains, for the benefit of readers with less of a background in mathematics, some of the basic concepts of the subject. A rough rule of thumb is that a topic belongs in part I if it is part of the necessary background of all mathematicians rather than belonging to one specific area. groups [I.3§2.1] and vector spaces [I.3§2.3] belong in this category, to take two obvious examples.

Vektorrum? Ja!!! Någon annan sa det här på pluggakuten också, men är det verkligen så...