Why does git mergetool open 4 windows in vimdiff? (I'd expect 3)

Question

When I met a conflict, I tried to use git-mergetool to solve it. I typed:

>git mergetool -t vimdiff

It opened vimdiff

Answer 1

Modifying a bit the commands from this page:

git config --global mergetool.vimdiff3.cmd 'vim -f -d "$LOCAL" "$MERGED" "$REMOTE"'
git config --global merge.tool vimdiff3

• 'Merged' would be your working copy.
• 'Local' the file that is in the branch you are trying to make the changes
• 'Remote' the file from the branch you are trying to merge with.

And then you execute the command: git mergetool.

Note: I use fugitive also and highly recommend it.