------------------------------
$ git config push.default current
$ git config remote.pushdefault myfork
-$ git checkout -b mybranch origin/master
+$ git switch -c mybranch origin/master
$ git rev-parse --symbolic-full-name @{upstream}
refs/remotes/origin/master
A = = A^0
B = A^ = A^1 = A~1
- C = A^2 = A^2
+ C = = A^2
D = A^^ = A^1^1 = A~2
E = B^2 = A^^2
F = B^3 = A^^3