Ah, that's a standard merge but a 3-way diff. Many DVCSs have that (including Mercurial). A 3 way merge would have "original", "version a", "version b", and "v

Ah, that's a standard merge but a 3-way diff. Many DVCSs have that (including Mercurial). A 3 way merge would have "original", "version a", "version b", and "version c", where "original" is the common ancestor of a, b and c. Mercurial disallows merges like this, but git supports them. I have no idea why git allows it. But yes, older VCSs ignored the "original" concept, which meant diff tools could just pop up "a" and "b". Which is just a way worse idea than including the original as well.