$ hg init

  $ echo This is file a1 > a

  $ hg add a

  $ hg commit -m "commit #0"

  $ echo This is file b1 > b

  $ hg add b

  $ hg commit -m "commit #1"

  $ hg update 0

  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo This is file c1 > c

  $ hg add c

  $ hg commit -m "commit #2"

  created new head

  $ hg merge 1

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ rm b

  $ echo This is file c22 > c

  $ hg commit -m "commit #3"