[teambayleaf]

> What's the source of this idea that "abstraction" means "combining duplicated code"?

It's coming from the tradition of Sir Francis Bacon's Empiricism. Some people believe that abstract ideas are mostly acquired thorough empirical observation a.k.a. carefully watching a series of repetitive events. The point here is that "to know" is a synonym of "generalization" for them. So OP naturally puts emphasis on duplicated code as a good opportunity for abstraction.

People from other camps have a very different view on human knowledge, and think that abstract ideas can indeed come from other sources, most importantly, from our reasoning function. For these people, the process of programming is to implement our innate idea into concrete code. For them, an actual piece of code is basically a "shadow" of our abstract concept.

Hell, someone really should write a book titled "The Logic of Programmatic Discovery" ;)