Query about mercurial heads diagram and heads counting - version-control

Question

I need to understand in which of the following lines the number of heads are change. Im finding it hard to understand what is going on in line 15..
I know that when a repository doesn't have the same change-sets when pulling or pushing from another repository so there is +1 head.
My diagram looks like this when i tried to solve it:
Line 12: push from clone2 to main repository
Line 15: push from Clone2 to Clone1 (because r3 doesn't similar to r1)
Line 17: pull r2 & r1 from main repository, since r1 and r3 already there, i've added r2 .
Total heads created: +3
main
repository: O--------r2
\----r1
Clone 1: O--------r1
\---r3
\---r2
Clone 2: O------r2---------r3
\--r1--/
The mercurial commands are below:
1: /home/user> hg clone http://remoteserver/mainrepository clone1
2: /home/user> hg clone http://remoteserver/mainrepository clone2
3: /home/user> cd clone1
4: /home/user/clone1> echo one > a.txt
5: /home/user/clone1> hg add a.txt
6: /home/user/clone1> hg commit -m "Added a file"
7: /home/user/clone1> cd ../clone2
8: /home/user/clone2> echo two > b.txt
9: /home/user/clone2> hg add b.txt
10: /home/user/clone2> hg commit -m "Added a file"
11: /home/user/clone2> hg pull ../clone1
12: /home/user/clone2> hg push -f
13: /home/user/clone2> hg merge
14: /home/user/clone2> hg commit -m "Merged"
15: /home/user/clone2> hg push -f ../clone1
16: /home/user/clone2> cd ../clone1
17: /home/user/clone1> hg pull

Answer 1

While planetmaker's answer in linked question is perfectly full and valid, I'll note some mistakes, omissions and wrong assumptions in this situation
Clone2 got head+1 on step 11
>hg pull ..\Clone1
pulling from ..\Clone1
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
Main got head+1 on step 12
>hg push -f
pushing to Z:\Main
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files (+1 heads)
http://i.imgur.com/KKNU39d.png
Clone2 got head-1 on step 14
Clone1 DOES NOT got head+1 on step 15 (mergeset pushed, with previous heads in Clone2 as parents of mergeset), at this step Clone1 is equal (in DAG-terms) to Clone2
>hg push -f ..\Clone1
pushing to ..\Clone1
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 1 changes to 1 files
http://i.imgur.com/9bY0URS.png
Steps 16-17 DO NOTHING, because Clone1 DAG is fuller than Main (it has mergeset from Clone2 on top of main-history)
>hg pull
pulling from Z:\Main
searching for changes
no changes found
In order to have full history in Main you must to push to it from any of clones (-f not needed and useless) to have mergeset as new single head in repository
>hg push
pushing to Z:\Main
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (-1 heads)