- Friends
- Co-workers
- Secret lovers
- Acquaintances of long standing
- Neighbors who know each others’ names
- Residents in the same or any similar zip code
- Members of a common geographic region
- Contributors to a gorgeous tapestry of domestic cultures
- Animals occupying adjacent ecological niches
- Symbiotic species
- Physical systems of the same body
- Cooperative microflora
- Complementary organelles
- Covalent bonds
- Quarks joined by the strong nuclear force into a hadron
- Generally speaking, any class of emergent phenomena based on chaotic interactions of linked elements exhibiting properties that individual elements do not possess
- People
