"Implications in mathematics" is a version of an old document used in lower-level courses. I forgot that the terminology "WI" was used in the document. It stands for "writing intensive", and in the context of lower-level courses, it asks the student to pay more attention to the exposition that we generally required at that level; the solution was to be written out carefully, as though it were to appear in a textbook, but without omitted steps. (To keep a textbook under 2000 pages, straightforward steps are often omitted.)
In this course, the aspiration is that the solutions to EVERY problem be written up carefully.
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Steven Zucker