There are seven pairs of circles that differ on the extent that they overlap. Other scholars have identified them as distinct phenomena that share overlap and commonalities. They often overlap horizontally, vertically, or both. There are many examples of nomenclatural overlap and differences of this sort. These groups overlap, but are not identical. In practice, many of these groupings may overlap. Ranges of females may overlap slightly with each other. These three areas obviously overlap quite frequently in chivalry and are often indistinguishable. In practice, elements of both systems overlap. Thus, the tracks partially overlap similar to roof shingles. These stages can overlap with each other. It allows a program to control multiple different flows of work that overlap in time. However, sometimes the two areas do overlap. These three areas obviously overlap quite frequently in chivalry, and are often indistinguishable. This may arise from human alteration of habitats enabling related allopatric species to overlap.