in the section “Various notions of cohomology expressed by Ext”:
corrected the definition of Lie Algebra cohomology, and slightly modified the group cohomology definition to account for arbitrary commutative rings
]]>added the statement (here), that sends both in the first variable and in the second variable to -s.
]]>for completeness I have added (here) statement of more examples of -groups of abelian groups (just going along Boardman’s lecture notes)
]]>Yes, thanks for the alert. I have fixed it now (here).
(And while I was at it, I also adjusted some of the formatting in the Definition.)
]]>In the subsubsection ‘1-Extensions over single objects’ it reads:
Should it not be:
?
]]>I have added to Ext a section Contravariant Ext on ordinary objects with the explicit definition by resolutions. But mainly I added after this a bit of explicit discussion of how to see that the standard formula computes indeed the homotopy classes .
More general abstract discussion along these lines is planned there or at derived functors in homological algebra, but is not done yes.
]]>Added a list of notions of cohomology expressible as Ext-groups to Ext.
]]>And a tiny little bit at Tor.
]]>tried to edit Ext a bit. But this needs to be expanded, eventually.
]]>