after 2 add ,1 rm cached ,commit first
master commit 2
branch dev commit 1
new src add  Hello.java
new Hi.java
aaa
merge master to dev ,resolved conflicts ok b-a.txt
miletone 1 over
create dev1
normal change;
Merge branch 'dev1'
change log
git branch -d dev
ai
ai
change
force commit
zouliangbu
yezou
aa