  Much initial research on automatic program repair has focused on experimental
results to probe their potential to find patches and reduce development effort.
Relatively less effort has been put into understanding the hows and whys of
such approaches. For example, a critical assumption of the GenProg technique is
that certain bugs can be fixed by copying and re-arranging existing code. In
other words, GenProg assumes that the fix ingredients already exist elsewhere
in the code. In this paper, we formalize these assumptions around the concept
of ''temporal redundancy''. A temporally redundant commit is only composed of
what has already existed in previous commits. Our experiments show that a large
proportion of commits that add existing code are temporally redundant. This
validates the fundamental redundancy assumption of GenProg.
