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Navee 你所说的这第三步 3.checkout a001 , 修改a文件提交一版a003 根本就不成立,git会提示
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.
If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:
git checkout -b new_branch_name
用checkout -b根本不会丢东西