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Section 18.1 Motivation
There are often situations where we want to group certain elements of a set together as being “the same.”
Example 18.1.1 .
At the end of this course, your instructor will assign each student a grade. In this system, every student who receives a “B” had roughly the same performance in the course (in principle, anyways). That is, consider the set of all students in this course — from the point of view of the grading system, the students in the subset of “B” students are all
equivalent in performance.
