Whitney published his theorem in 1934, while Sobolev introduced his spaces in the 1960s (though I think other mathematicians may have been using some version of what we now call Sobolev spaces prior to this). So I would presume the Sobolev space extension theorem was discovered after Whitney’s theorem.

Fefferman and his coauthors have also worked on Sobolev extension problems (in Sobolev spaces with more than one degree of regularity), see e.g. http://www.ams.org/journals/jams/2014-27-01/S0894-0347-2013-00763-8/home.html . So presumably there is a relationship between the two extension problems, though I have not studied these works in detail.

]]>When you attend talks….do you in general take notes? Is this a good practice?

Thanks

]]>Thanks for the post and for your great blog!

I noticed some typos :

1. In the first equation which is not inline (the norm of F) you want j to play some role in the RHS.

2. Two sentences above the last QUESTION, F should be f and the inclusion should hold for all x in E.

Perhaps the typos are in my head, if so I apologize. ]]>