Instead of manually backtracking what changes each developer made, three-way merge does just that for us! This is because modern version control systems, such as Git, can automatically find what's known as the "nearest common ancestor", aka base revision (or merge-base). It is called "3-way" since it uses three revisions to produce a final merged version.

Whenever two or more developers make changes to the same file respectively and later try to fuse the versions, merge conflicts will likely occur.

Strange result: null vs 0