+--
+
+History Simplification
+~~~~~~~~~~~~~~~~~~~~~~
+
+When optional paths are given, 'git-rev-list' simplifies commits with
+various strategies, according to the options you have selected.
+
+Suppose you specified `foo` as the <paths>. We shall call commits
+that modify `foo` !TREESAME, and the rest TREESAME. (In a diff
+filtered for `foo`, they look different and equal, respectively.)
+
+In the following, we will always refer to the same example history to
+illustrate the differences between simplification settings. We assume
+that you are filtering for a file `foo` in this commit graph:
+-----------------------------------------------------------------------
+ .-A---M---N---O---P
+ / / / / /
+ I B C D E
+ \ / / / /
+ `-------------'
+-----------------------------------------------------------------------
+The horizontal line of history A--P is taken to be the first parent of
+each merge. The commits are:
+
+* `I` is the initial commit, in which `foo` exists with contents
+ "asdf", and a file `quux` exists with contents "quux". Initial
+ commits are compared to an empty tree, so `I` is !TREESAME.
+
+* In `A`, `foo` contains just "foo".
+
+* `B` contains the same change as `A`. Its merge `M` is trivial and
+ hence TREESAME to all parents.
+
+* `C` does not change `foo`, but its merge `N` changes it to "foobar",
+ so it is not TREESAME to any parent.
+
+* `D` sets `foo` to "baz". Its merge `O` combines the strings from
+ `N` and `D` to "foobarbaz"; i.e., it is not TREESAME to any parent.
+
+* `E` changes `quux` to "xyzzy", and its merge `P` combines the
+ strings to "quux xyzzy". Despite appearing interesting, `P` is
+ TREESAME to all parents.
+
+'rev-list' walks backwards through history, including or excluding
+commits based on whether '\--full-history' and/or parent rewriting
+(via '\--parents' or '\--children') are used. The following settings
+are available.
+
+Default mode::
+
+ Commits are included if they are not TREESAME to any parent
+ (though this can be changed, see '\--sparse' below). If the
+ commit was a merge, and it was TREESAME to one parent, follow
+ only that parent. (Even if there are several TREESAME
+ parents, follow only one of them.) Otherwise, follow all
+ parents.
++
+This results in:
++
+-----------------------------------------------------------------------
+ .-A---N---O
+ / /
+ I---------D
+-----------------------------------------------------------------------
++
+Note how the rule to only follow the TREESAME parent, if one is
+available, removed `B` from consideration entirely. `C` was
+considered via `N`, but is TREESAME. Root commits are compared to an
+empty tree, so `I` is !TREESAME.
++
+Parent/child relations are only visible with --parents, but that does
+not affect the commits selected in default mode, so we have shown the
+parent lines.
+
+--full-history without parent rewriting::
+
+ This mode differs from the default in one point: always follow
+ all parents of a merge, even if it is TREESAME to one of them.
+ Even if more than one side of the merge has commits that are
+ included, this does not imply that the merge itself is! In
+ the example, we get
++
+-----------------------------------------------------------------------
+ I A B N D O
+-----------------------------------------------------------------------
++
+`P` and `M` were excluded because they are TREESAME to a parent. `E`,
+`C` and `B` were all walked, but only `B` was !TREESAME, so the others
+do not appear.
++
+Note that without parent rewriting, it is not really possible to talk
+about the parent/child relationships between the commits, so we show
+them disconnected.
+
+--full-history with parent rewriting::
+
+ Ordinary commits are only included if they are !TREESAME
+ (though this can be changed, see '\--sparse' below).
++
+Merges are always included. However, their parent list is rewritten:
+Along each parent, prune away commits that are not included
+themselves. This results in
++
+-----------------------------------------------------------------------
+ .-A---M---N---O---P
+ / / / / /
+ I B / D /
+ \ / / / /
+ `-------------'
+-----------------------------------------------------------------------
++
+Compare to '\--full-history' without rewriting above. Note that `E`
+was pruned away because it is TREESAME, but the parent list of P was
+rewritten to contain `E`'s parent `I`. The same happened for `C` and
+`N`. Note also that `P` was included despite being TREESAME.
+
+In addition to the above settings, you can change whether TREESAME
+affects inclusion:
+