$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0" -d "1000000 0"
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1" -d "1000000 0"
$ 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" -d "1000000 0"
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" -d "1000000 0"