Good!
A - B - C - D <develop>
\
E - F - G <PR1>
\
H - I - J <PR2>
Diverged!
A - B - C - D <develop>
\
E - F - G <PR1>
E' - F' - G' - H - I - J <PR2>
Want to get rid of E', F', G'
, they are out of date.
git rebase --onto <new base> <old base>
. We want to rebase using new base PR1
and keep H, I, J
(H~4): git rebase --onto P1 HEAD~4