Currently we compare fiber identifiers when identifying the common ancestor of two fibers. However, in certain circumstances the order of fiber identifiers could not reflect the order in which fibers were created, for example if the system time was changed.

Since we are looking for the common ancestor between two fibers, we can instead reason that up to the common ancestor the ancestry of the two fibers must be the same and thus must have the same depth. So instead of comparing fiber identifiers we can simply drop an element from the longest ancestry if we haven't gotten to a common ancestor yet, or both if the depth is the same and we haven't gotten to a common ancestor yet.