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1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeSep 2nd 2012
   • (edited Sep 24th 2012)
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   Author: Urs
   Format: MarkdownItexthought we'd need an entry _[[homotopy category of chain complexes]]_

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

2. • CommentRowNumber2.
   • CommentAuthorjim_stasheff
   • CommentTimeSep 3rd 2012
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   Author: jim_stasheff
   Format: Textperhaps with a distinction from and/or link to higher homotopies

   perhaps with a distinction from and/or link to higher homotopies
3. • CommentRowNumber3.
   • CommentAuthorUrs
   • CommentTimeSep 24th 2012
   • (edited Sep 24th 2012)
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   Author: Urs
   Format: MarkdownItexI 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: * [[category with translation]] * [[triangulated category]] (and all the related, such as [[enhanced dg-category]]) Will be further working on _[[derived category]]_ now.

   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:

   • category with translation

   • triangulated category (and all the related, such as enhanced dg-category)

   Will be further working on derived category now.

4. • CommentRowNumber4.
   • CommentAuthorUrs
   • CommentTimeSep 24th 2012
   • (edited Sep 24th 2012)
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   Author: Urs
   Format: MarkdownItexI 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](http://ncatlab.org/nlab/show/homotopy+category+of+chain+complexes#ChainHomotopiesThatOughtToExistButDoNot)_. It could probably go elsewhere just as well.

   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.