SHELL

git checkout stack

@{-1} is a way to refer to the last branch you were on. This is
accepted not only where an object name is expected, but anywhere a branch name is expected and acts as if you typed the branch name.
E.g. git branch --track mybranch @{-1}, git merge @{-1}, and
git rev-parse --symbolic-full-name @{-1} would work as expected.

and

git checkout - is a shorthand for git checkout @{-1}.