ctrl-tab is just cycling over tabs. Ctrl-u is more what I'm looking for, but it's history buffer is limited to just one file. In fact what I'm looking for is a super Ctrl-U for all previously opened files. The classical use case is :
0/ I work on file F0, and I see an unknown function P1?
1/ I jump to declaration of function P1 in file F1 line l1
2/ I jump to declaration of function P2 in file F2 line l2 used in P1
3/ I use "back" to go from F2:l2 to F1:l1
4/ I use "back" to go from F1:l1 to my original position in the file I was editing
This kind of function is a must with huge professional projects.