[p4] help with merging/integrating between branches

[Andy Nguyen]

Greetings,

I have a few questions regards to merging/integrating between branches in
Perforce.

Let's say I have branch B1, and branched out for B2.  Then create B3 off B2.

B1
-----------------------------------------------------------------------------------------B1
        \
         ----------------------------------------------------------------B2
                  \
                   -----------------------------------B3
                        \             \
                          \            ---------------------------B3.1

--------------------------------------------------B4

I can easily merge all changes back to the parent branch (i.e.: from B2 to
B1, and B4 to B3), and the cmd that used is "p4 integrate -r -b B1B2" or "p4
integrate -r -b B3B4.   Please notes that B1B2 and B3B4 are my branch spec,
which I created when the branch is generated.

Is there a way to merge back to the "grand-parent" branch in Perforce?  I
would like to merge all changes from B3 back to B1, and B4 back to B1.
Since I don't have a branchspec, how can I proceed?  For example, I would
like to merge all changes from B3 back to B1.

Many thanks in advance, and I really appreciate for your help.

Regards,
-Andy