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• CommentRowNumber1.
• CommentAuthorUrs
• CommentTimeSep 2nd 2012
• (edited Sep 24th 2012)

thought we’d need an entry homotopy category of chain complexes

• CommentRowNumber2.
• CommentAuthorjim_stasheff
• CommentTimeSep 3rd 2012
perhaps with a distinction from and/or link to higher homotopies
• CommentRowNumber3.
• CommentAuthorUrs
• CommentTimeSep 24th 2012
• (edited Sep 24th 2012)

I have expanded homotopy category of chain complexes by adding a few basics.

In the course of this I have also touched the formatting of the following entries:

Will be further working on derived category now.

• CommentRowNumber4.
• CommentAuthorUrs
• CommentTimeSep 24th 2012
• (edited Sep 24th 2012)

I needed to spell out somewhere a very basic expositional example of what goes wrong in $\mathcal{K}(\mathcal{A})$ that is rectified in the derived category such that the example roughly motivates the idea of projective resolutions. I ended up putting it here into a new section Examples - Chain homotopies that ought to exist but do not. It could probably go elsewhere just as well.