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<p>created <a href="http://ncatlab.org/nlab/show/nonabelian+group+cohomology">nonabelian group cohomology</a></p>
<p>the secret title of this entry is "Schreier theory done right". (where "right" is right from the <a href="http://ncatlab.org/nlab/show/nPOV">nPOV</a>)</p>
<p>this is the first part of the answer to</p>
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What is going on at <a href="http://ncatlab.org/nlab/show/nonabelian+Lie+algebra+cohomology">nonabelian Lie algebra cohomology</a>?
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<p>The second part of the answer is the statement:</p>
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The same.
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<p>;-)</p>
<p>I'll expand on that eventually.</p>
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Accompanying article group extension focusing on Schreier's theory for nonabelian group extensions traditional way. Added also an entry within my personal lab about Paul Dedecker (zoranskoda), one of the pioneers.
went again through nonabelian group cohmology and tried to carefully match all formulas (concerning precise order of the terms and points where the automorphism actions apply) to the diagrams, following the "convention L B" as detailed at strict 2-group - in terms of crossed modules.
Should be right now. Mistakes here are like sign errors. Not terribly important in general, but sometimes very important, and usually annoying to track down.
added at nonabelian group cohomology a section Homotopies between 2-cocycles.
To be compared with Zoran's Comparing different extensions: 2-coboundaries at group extension
I created a bit by an error connection on a comodule thinking on comodules over additive comonads. But for now the material still fits into the connection for a coring so I left only a redirect FOR THE MOMENT at connection on a comodule and expanded entry connection for a coring, having also few words on comonad case. Today I largely expanded group extension with a 2-coboundary section and more, on the basis of my LaTeX notex from 1997 and being stimulated by discussions with Urs. I now also created monadic descent and symmetric comonad.
You plan to write something else at connection on a comodule, which is why the redirect is only temporary?
I hope so, but I am yet not clear about how the grand scheme will work. Once the material is built up, this will be easier to do then at this point.
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