From: Mathieu Bouchard <matju@...>
Date: 2000-12-04T01:20:52+09:00
Subject: [ruby-talk:6772] Re: Array Intersect (&) question

> is natural intersection.  Both make me suspect easy implementation.
> Probably proper intersection is '(1 2) for this case.

If we're implementing Sets using Arrays, yes. There is another formalism
called MultiSet. I don't know how it works (in math textbooks), but
intuitively I'd say:

in A,   e appears x        times
in B,   e appears y        times
in A&B, e appears min(x,y) times
in A|B, e appears max(x,y) times

however I *don't* advocate changing the behaviour of Array.

matju