how do I continue a merge after resolving conflicts?

[Jamie Wilkinson]

This one time, at band camp, Martin Pool wrote:
>For those following along at home: bzr merge always merges all files,
>leaving conflicts in those where they occur.  There's no need to do
>another merge from the same source after you resolve the conflicts --
>just fix them up and commit.

So, bzr aggregates all the changesets coming in the merge, and applies it
once?  Or is it possible that two incoming changesets can conflict with a
local changeset, and make a mess of the << == >> ?